First Rain Band On Saturday AM

Am writing this at 7 am on Saturday morning, 9 February 2013. At this time the first rain band has moved on to the east of the house. Between about 5:30 and 6:45 am MST there was 0.07" of rain here, and I see that the snow level was very low on the foothills. I show two radar products here from the KIWA radar (these have come from the College of DuPage - CoD link to right - weather site). The top image is precipitation type at about 6:35 am - this is one of the products available from the dual polarization upgrade. The CoD radar page has many of these polarization products available, which is a real plus, since they are not shown at the NWS radar pages. Precipitation type indicated in the image is DS (dry snow). But wait, it was raining here. Unfortunately, the NWS KIWA radar is sited at over 5,000 ft MSL out in the Empire Mountains. So, the radar beam is always substantially above the low elevation locations here in the metro area, thus the radar indicates only snow. This illustrates one of the problems of siting the radars at high elevations (there is a separate set of problems that would occur were the radar down here in the low elevation areas).

The product below is the VAD winds aloft time-series, another product that can be examined at the CoD web page. This product shows the strong west-southwesterly winds aloft over eastern Pima County. Note that the lowest winds are obtained at 6,000 ft MSL. Regardless, the CoD site is one that I go to if I want to examine radar data in more detail than I can at the NWS web pages.

Moisture-Starved System Approaches

A quick look at the approaching system. This morning's 12 UTC NAM analysis at 500 mb (above) indicates a cold and complex system - center of circulation is near San Francisco but a strong vorticity maximum is approaching Las Vegas. A stronger vorticity maximum is over the ocean west of San Francisco. Temperatures at 500 mb, near the core of the system, are below -30C, so definitely a cold event.

As per the last several systems, this one is also starved for a decent moisture feed. Both the Mimic (above from CIMSS for 09 UTC) and CIRA (below for 11 UTC) blended PW products show an inflow plume near San Diego, but with values only reaching to around 20 mm.

The early run of the WRF-GFS forecasts best band of precipitation (above is the forecast, composite radar image valid at 8 am Saturday morning) across eastern Pima County tomorrow morning. The surface plot forecast for the same time (below) indicates a raw morning with northwest winds, temperatures in the 30s and light rain showers. It will be quite a change! Total WRF-GFS forecast precipitation through midnight Saturday night is at the bottom, indicating light amounts, except in the mountains and higher elevations east and southeast of Tucson. Snow levels will come quite low along parts of I-10 and Highway 83, but ground and pavement will start out very warm. Some driving caution may be needed.

A Look At WRF-GFS For Friday And Saturday

This morning the 500 mb analysis for 12 UTC indicates that the next system to impact the Southwest is currently off the coast of British Columbia. The temperatures in the core of this system are currently around -35C, fitting with the forecast for a serious cool down on the weekend. Most weather attention remains centered on finding Nemo. However, there will be interesting weather out in this part of the country also.

I have just taken a quick look at the forecasts from the early run of Atmo's WRF-GFS model. The forecast surface plot (above) for 4 pm MST on Friday afternoon, indicates warm temperatures but with strong and gusty south-southwest winds. The front moves through quickly during the night and by 9 am on Saturday morning the forecast radar echoes (below) indicate a post-frontal band of showers moving across eastern Pima County - this is the first of several bands forecast during the day Saturday.

The surface conditions forecast at 10 am on Saturday (above) indicate damp and much cooler temperatures - note that there are some temperatures down in the 30s on the north and east sides of the metro area. The forecast of total precipitation through midnight on Saturday night is shown below. This event is currently forecast to be a light precipitation situation, except over the higher elevations of the Catalinas and Rincons..

Northeast Storm Named Nemo by TWC

The Weather Channel has named the forecast big Northeast storm Nemo. The cyclone, assuming it comes together as forecast by the models, will bring a serious snowstorm to much of the Northeast. This naming of winter storms is something the Weather Channel is doing for the PR hype.

Below is the 8 am MST surface analysis from the NWS HPC. Where is Nemo if you want to track him? Too soon - Nemo's not on the map yet. The storm is expected to develop on Friday as short waves in the southern and northern streams merge and a deep low develops rapidly along the East Coast.

Next Weather System

The first weather system of February struck over the past weekend and brought an extended period of thick middle and high clouds, and that was it. However, the next system looks a bit more interesting (but nothing like the major storm forecast for the Northeast). There are also significant differences in the model forecasts

at 96-hours (i.e., valid at 5 am MST on Saturday morning 9 February). The NWS GFS forecast at 500 mb valid at that time (above) indicates an elongated short wave that stretches from southern Canada to southern California. The ECMWF forecast valid the same time, however, predicates a significant closed low over the Great Basin with a strong vorticity maximum over central Arizona. The ECMWF forecast would bring a strong Pacific front through southeastern Arizona late Friday afternoon with wind, dust, and possibly showers along the front. The GFS forecasts a less distinct front and no precipitation for southeast Arizona. Both of these forecasts are from the operational members of the two models.  Both models forecast much colder thicknesses by Saturday and it will be interesting to see if the faster and stronger ECMWF forecast verifies better than the GFS forecast. The ECMWF heights at 500 mb are about 120 m lower than the GFS over central Arizona on Saturday morning.

Dr. John Jeffries

John Jeffries, a Boston physician and scientist, is sometimes said to be the country's first “weatherman.” He was born on February 5th in 1744, and, in his honor, today is National Weatherperson’s Day.

However, more people are probably aware that this is also National Pancake Day. For the eighth year, IHOP restaurants are offering a free stack of buttermilk pancakes today from 7 a.m. to 10 p.m.

More News Re The NWS RRS Sondes

Back on July 18, 2012 I reported that:

The efforts to replace the the problem-plagued Mark IIA sondes of the NWS RRS program are moving ahead, after the testing reported above. A Technical Implementation Notice indicates that 5 more NWS upper-air sites will begin using the Vaisala RS92 GPS sondes on or about March 1st. The sites are Morehead City, NC, (72305); Santa Teresa, NM, (72364); San Juan, PR, (78526); Gaylord, MI, (72634); and Medford, OR, (72597).

Apparently, while the transition to the the RS92 sondes is occurring, other NWS upper-air sites will be using the Sippican LMS6 (rather than the MarkIIA) sonde. The LMS6 uses an improved humidity sensor.

Pacific Moisture Inches Northward

First - brief January summary: TUS had 12 days during January with lows of 32F or colder. Here in the Rillito Bottoms we had 20 such days, with 4 mornings down in the teens. Rainfall at TUS was 0.81" and here at house we had 0.76". Not an exciting month, except for the cold snap.

Very chopped up setting this afternoon in upper-troposphere, with several weak short waves moving different directions along and off the U.S. and Mexico west coasts - above water vapor image is from 3 pm MST. The MIMIC blended PW (below from 2 pm MST) shows that higher values of PW have moved northward, with values of over an inch nearly reaching San Diego.

As a weak middle-level short wave affects Arizona during the day tomorrow, the models forecast a bit of precipitation. The 5 am forecasts from the WRF-GFS indicate widespread radar echo coverage at noon tomorrow (below - Sunday 3 February). These are mostly mid-level echoes with light showers and virga.

The forecast for total precipitation through 5 pm tomorrow (below) shows widespread coverage of very light amounts, with the mountains doing slightly better.

And least I forget, it's a special day today!

From Mike Leuthold

Bob,

    I've returned to astronomy after almost 30 year hiatus so I'm much more interested in the WRF cloud forecasts than I was previously.  It does a pretty good job normally.  Last night, it was forecasting clearing in the early evening thus I set up my equipment.  By about 8:30 the high clouds did move off to the east and I was able to take these images.
    The forecast for the next few days looks really bad as you have pointed out-WRF is forecasting frequent high clouds.  Too bad as the moon has just left the evening sky so it's perfect for astro-photography and observing. It will make for nice sunsets though.

Mike

High Clouds In The WRF-GFS Forecast

The Outgoing Long wave Radiation (OLR, in watts per square meter) product can be used to evaluate the model's forecast of cloudiness. The model keeps skies mostly clear today until late afternoon and evening, and then brings a large patch of high clouds in from the Pacific during the night (below is OLR forecast valid at 6 am tomorrow morning) with gray-scale indicating watts per square meter. Low OLR indicates increased cloudiness, while high values indicate clear skies. So the model is forecasting significant high-cloudiness during the night tonight. If this verifies, it will keep low temperatures mild (the early WRF-GFS forecasts lows next two mornings at TUS to be in the 50s, i.e., considerably milder than this morning).

During the day tomorrow the clouds move away and the forecast for OLR at 3pm (above) indicates mostly clear skies again. But, by midnight tomorrow night (below) the model has forecast an even larger area of cirrus across southern Arizona. Timing and duration are everything with these patches of cloudiness wrt both high and low temperatures.

First day Of February In Tucson

February dawns with beautifully clear skies here in Tucson and southeast Arizona. Low temperatures here in the north part of the city are again in the upper 20sF, so it's quite chilly out right now. Low at house was 28F and there is frost out there on roofs and cars, but it will warm up quickly.

The main forecast problem today and tomorrow will be the timing of high-level cloudiness coming by from west and southwest of Baja. Above is the water vapor image from 6 am this morning, showing a very large area of middle and upper-level cloudiness from south of 10 degrees north to about 30 degrees north.

The MIMIC blended precipitable water (above, from CIMSS in Madison, Wisconsin) for the eastern Pacific shows that PW values are low north of 20 degrees latitude (except far to the west). This means that the clouds of interest for the Southwest are high and that low-levels are dry. So, the main forecast impacts today and tomorrow will be the timing of cloudy periods and their impact on temperatures. Will look at the WRF-GFS forecast of OLR in next post.

Tree Damage From Cold Spell

During January, from the 13th through the 16th, we had morning low temperatures from 14 to 18F. The palm trees, and some other kinds, are looking pretty bad now with obvious damage. The palms looked like this after the February 2011 cold spell but revived when the summer rains arrived. Hopefully that will be the case this year also.

Brief Summary Of Past 24-Hours

Yesterday's frontal passage  produced cold winds (30 to 40 mph - Guthrie RAWS came in with 53 mph) and periods of light showers. The ALERT network shows mostly light amounts for the past 24-hours over both the west (above) metro area and also to the east (below). There were only four reports of a quater of an inch or more. About 60% of the ALERT stations had measurable rainfall. However, this is a bit misleading since some stations, e.g., Manning Camp, had only snowfall, which is not measured. Here at the house there was 0.05" in the gauge this morning, with a morning low of 35F. Atmo also had 0.05", while TUS had 0.06" and DM AFB had 0.03". Bottom image shows some snow cover at Bisbee this morning.

Early Morning Severe Thunderstorms

Severe thunderstorms early this winter morning are occurring over the southern Plains. Above is base scan from NWS Tulsa radar a bit after 7 am (29 January 2013). There are currently two tornado watches out from southwestern Oklahoma into southwestern Missouri. There is a moderate risk area for later today, centered over Arknasas. A major winter storm is expected as an intense low develops toward the western Great Lakes region.

A Little Bit Of Everything

We have had a number of light showers here at house this early afternoon (Monday January 28th) with gusty winds of 20 to 30 mph. The temperature has fallen to 46F, so it is quite raw out.

The very low rainbow above was along the foothills of the Catalinas at a bit after 2 pm MST, while the snow was flying up on Mt. Lemmon (below) a bit before 3 pm. At the same time skies were sunny out at Kitt Peak (bottom).

January Closes Out With A Fairly Dry Evenet

The current surface plot (above from NCAR RAL) for a bit after 6 am MST shows that the approaching cold front is about half way across Arizona. Precipitation is mostly confined to northern parts of the state. Snow has returned to Flagstaff and the Grand Canyon area after the heavy rains of the weekend. Gusty winds behind the front for much of the state today.

The blended PW product from CIRA at Colorado State is shown above for 5 am MST this morning. This analysis indicates that the current system is fairly starved for moisture, with amounts of 0.50 inch just into southeast Arizona (the light blue indicates amounts over half an inch). Much different than Saturday's system which had significant moisture inflow from low latitudes.

All of the GFS ensemble members (from forecast run initialized at 5 pm MST yesterday) forecast precipitation across southeastern Arizona for period ending at 5 pm this evening. However, Atmo's early run of the WRF-GFS, with its high-resolution grid, indicates that most of that precipitation is from the
coarse grid GFS smoothing mountain precipitation into lower elevations. So it looks windy and cooler, with some light showers about. Some spots in the lower elevations may get enough rain to wet the roads while other places will get spits and sprinkles, as more significant amounts stay at higher elevations.

In the longer range, some GFS members are predicting a system at 8-9 days that taps into low latitude moisture - but of course, that's off in February.

Next Event Approaching

Yesterday's rain event had ended here at the house by noon, but there were isolated showers around during the afternoon and evening, especially out to the northwest and also east of Tucson. The Atmo WRF-GFS predicted the pattern of the rainfall across southeast Arizona well, although the amounts were somewhat under-forecast. Rainfall here at the house ended up at 0.59". With amounts over an inch in the Catalinas, the Rillito Wash was flowing yesterday afternoon - the first time in quite a long while. Morning view of Catalinas from campus (top) and just below shot from Mt. Lemmon showing the snow mostly gone after the rain.

The next system will move in tomorrow with a strong and cold 500 mb short wave sweeping across Arizona. The early run of the WRF-GFS moves the cold front by before noon and has showers affecting mostly the high elevations areas of southeast Arizona. The forecast above is on the 5.4 km domain (total precipitation valid at midnight tomorrow night) and indicates the focus again on the Rim country. David Blanchard reported the heavy rains yesterday at Flagstaff were eating away the snow cover up there - next system should replace some of it.

The high-resolution forecast of total precipitation on the 1.8 km grid (below, also valid at midnight Monday night) indicates very light amounts at some some lower-elevation spots in Pima County - all-in-all the WRF forecasts a rather wimpy precipitation event here in the southeast part of state.

Rain Event Well Underway

Very substantial plume of tropical/subtropical moisture extends into much of Arizona and southern California this morning. Above is 12 UTC blended PW product from CIRA/Colorado State and below is 10 UTC MIMIC PW product from CIMSS at Univ. of Wisconsin. The MIMIC product shows the moisture plume extending northward to the central California coast, where it is interacting with a narrow atmospheric river coming from north of Hawaii. Rain amounts already are at 0.50 to 0.75 inches in the mountains, with amounts reaching to around 0.33" at some places in the metro area.

The early WRF-GFS forecast of precipitation through midnight tomorrow night (27 January 2013) is shown above - with a major event indicated for the higher elevations of northern Arizona with a focus on the Rim north of Payson. The latest NAM forecast of precipitation ending at same time is below. It appears that both models continue to under-forecast rainfall amounts for our part of the state (we are now around 0.35" here at the house).