Looking Toward Early Next Week

This morning the short wave at 500 mb that will impact the Southwest on Monday and Tuesday next week is embedded somewhere within a very complex pattern over the northern Pacific. The above graphic is this morning's 500 mb analysis from the NWS NAM model, showing an elongated cyclone stretching east to west along about 45 to 50 degrees latitude, north of a strong, zonal height gradient. By 84-hours (below - valid at 5 pm MST Monday 8 April) the NAM morning forecast indicates that a strong split in the 500 mb flow has occurred west of Canada, as a substantial short wave and closed low dug from the Pacific system into the Southwest. Maximum vorticity at this time is forecast within a filament from northwestern New Mexico westward across southern Arizona. If this forecast verifies, we'll have experienced a strong frontal passage across the metro Tucson area sometime Monday morning.

The 96-hour spaghetti chart for 500 mb (also valid 5 pm Monday) above shows largest spread (i.e., highest uncertainty) over North America extending from the southern California coast northeastward to Hudson's Bay. However, the local NWS has already made deterministic, point forecasts of winds and gusts they expect on next Monday - see weather cartoon below. I don't think that I recall seeing such strong winds, including gust speeds, forecast so far out in time for southeast Arizona. Will continue to monitor the evolution of this interesting system.

First Weather System Of April 2013 For Southwest

The first weather system of April will affect the Southwest early next week. At this time the global models are bouncing around inconsistently on how strong the associated 500 mb short wave will actually be. The ECMWF has been weaker and farther north on the forecasts from 12 UTC versus those from 00 UTC. Shown above is the ECMWF 144-hour 500 mb forecast from 12 UTC yesterday morning, while the same forecast from 00 UTC last evening is shown below. Heights over southeastern Arizona are around 120+ m lower in the forecast below (note there is a 12-hour difference in the verifying time of the two forecasts).

The GFS ensmble forecasts from 00 UTC last evening also have a considerable spread for the Southwest - two of the 144-hour ensemble 500 mb forecasts are shown above and below. The stronger forecast (below) indicates 500 mb heights around 180 m lower near Tucson than the weaker forecast above. So, considerable uncertainty remains regarding the evolution of this system. It appears that we can expect cooler and windy conditions Monday afternoon and Tuesday, but the likelihood of showers and degree of cool-down remain uncertain - the GFS forecasts from 00 UTC indicated showers for southeast Arizona on only 3 of the member forecasts. So, it's wait and watch at this time.

NAM Verifies Well With This MCS

A quick look at how the NAM did with its 24 and 48-hour forecasts of the Gulf Coast MCS. Model verified quite well this morning (refer to previous post). With an MCS about where and when was forecast. System producing mainly heavy rains as it moves rapidly east. Above is 12 UTC water vapor image and below is base-scan radar for 12 UTC (both from NCAR RAL).

Above is storm total, radar-estimated rainfall at 13 UTC from NWS New Orleans/Slidell (KLIX) - note large area of 2 to 5+ inches west through south of the radar. Below is 3.5 degree tilt showing a very nice bright-band ring (both of these radar images from CoD web page).

NAM Again Forecasts Significant MCS

While I was browsing through the model forecasts yesterday morning, I noticed that the 48-hour NAM forecasts indicated a substantial MCS over Louisiana and the northern Gulf of Mexico at 12 UTC on the morning of April 3rd (tomorrow morning - see above NAM forecast of radar echoes). This morning's new forecast, valid the same time tomorrow morning, continues to predict a significant MCS in the same general location - see current NAM radar forecast below for 24-hours.

The 24-hour 700 mb forecast for tomorrow morning (above) indicates a substantial field of upward motion that has been generated by both low-level warm advection and mesoscale convective circulations. The NAM model forecasts heavy rains with this MCS and, depending on the evolution of CAPE, it may be a severe weather producer too. Most interesting is that the model forecasts a very long fetch from the Caribbean and Bay of Campeche for the low-level jet (below is 850 mb forecast of winds and precipitable water for 12 UTC tomorrow). Moisture values are high and substantial low-level moisture and warm temperature advection is forecast into the area of the MCS. Given the forecast consistency,  perhaps the model will do better in this situation than the MCS forecast discussed in an earlier post?

NOAA Hires High-Level Director Of Graphics

As many know, NOAA and its NWS have moved into the highly competitive arena of social networks, such as YouTUBE and Facebook - for example, see banner above. The agency has hired a well-known author and illustrator, Mr. B. Breathed of California, to become the NWS Director of Graphics. The new Director will be responsible for growing a larger NWS audience that follows and "likes" the agency on the various social media. It is expected that numerous cartoon templates, with weather and climate themes, will be developed for use at all NWS Offices, bringing a uniform flavor and quality to the agency's social network presence.

There are some rumors that a well-known and popular penguin, an excellent avatar for climate change, will likely replace the aging NOAA sea gull on the agency logo - see below.

The Tri-State Tornado

A number of meteorologists have been working on re-analyses of the conditions associated with the Tri-State tornado of March 1925. The project has dragged out to more than a decade, but I can happily report that our paper on the supportive meteorological conditions has just been published in the the EJSSM.

The paper can be found at:         http://www.ejssm.org/ojs/index.php/ejssm/article/view/114/88

Our paper on the re-analysis of the damage track and related issues will appear shortly.

Sun Comes Out For Easter

Late in the day yesterday Tucson finally got a bit of sun before dark - above image is from 6 pm. This morning, Easter Sunday - 31 March, is dawning clear and sunny, as image looking north from Kitt Peak (below) shows at around 6:30 am.

Obviously, March is coming to a close after producing almost nothing in the way of precipitation for the Tucson area. Only rainfall here at the house was 0.03" on the 9th. Compared to last March, this past month has been dry and also warmer - wrt morning lows. During March 2012 there were 19 mornings here at the house with lows below 40F, 8 mornings with freezing or below, and 5 mornings with lows in the 20sF. This month there were only 9 mornings with lows below 40F and 1 day (the 1st of March) with a low below freezing (29F). Quite some difference between the two years! April 2012 brought 6 days in the 30s, as well as the year's first 100+ high - we'll see what this year has in store for us.

There continues to be little on the weather horizon. It has been interesting watching the ECMWF the past 5 days or so. That model has continued to forecast an interesting weather pattern, with a 500 mb closed low over the Southwest. However, the interesting pattern has continued to be forecast out at day 9 or 10 - thus, the next weather-maker has not gotten any closer. The 500 mb ECMWF forecast below is valid at 00 UTC on April 10th. This seems, at least to me, to be somewhat unusual behavior for the European model.

Gloomy Start To Easter Weekend

Middle and high clouds streaming into the Southwest are making for a dreary start to the Easter weekend. Above is 7 am MST view of the Catalinas from campus. Below is 8 am MST water vapor image showing larger, upper-tropospheric low spinning well west of central California, with a long fetch of moisture into the Southwest from low latitudes.

The blended PW product from CIMSS at Univ. of Wisconsin (above for 5 am MST) indicates higher PW values of over an inch approaching Baja and southern California. However, the forecast models do little with the moisture increase, except well to the north, as the system comes in across the Great Basin from the Pacific. Below is today's early morning forecast from the Atmo WRF-GFS model on the 5.4 km domain. The forecast is of total precipitation through midnight on April 1st. The model keeps most of Arizona dry through this period. The morning soundings do indicate that some slight bits of middle-level CAPE may be coming by today, so the month may bow out with some more virga aloft.

Dearth Of Weather Continues

The lack of weather continues here in the south of Arizona. There was a stacked, lenticular cloud over the Catalinas before sunrise, but by the time there was enough light for a photograph it had dissipated. The folks at the NWS Forecast Office may be bored also.

The above is yesterday's graphic for the Easter weekend. What can I say?

On a more meteorological note - I noticed mid-level buildups to the southwest when I walked this morning. Some had just enough vertical extent to produce ice-crystal virga. The 8 am MST visible satellite image above captures this cloud field. The Tucson sounding this morning - skewT plot below - indicates that a layer just below 500 mb may have a tiny sliver of CAPE. I know I'm really stretching to find something to write about, but that's pretty much been the story here since March 10th. So it goes.

Spring Snowstorm

Very heavy snows in eastern Colorado yesterday with accumulations of 1 to 3 feet along the northern Front Range. Above is near whiteout at Denver International Airport, which is out in a very exposed location.

The surface low has moved to the Missouri Bootheel this morning, bringing tough travel conditions along I-40 from Topeka to St. Louis - above is 14 UTC surface chart from College of DuPage. Below is graphic showing current NWS warnings etc. The big band of "pink" is area under winter storm warnings.

How Did 72-Hour NAM Forecast Do?

The NAM 72-hour forecast of radar echoes valid for 1200 UTC this morning (Saturday March 23rd) is shown above in the middle graphic. The 1145 UTC WV satellite image is at top and the regional radar at 1220 UTC is just above. The model had the right idea but was off some in space, with the verifying storms to the south and southeast over northern Alabama and Georgia. Model forecast was too strong also, but all-in-all not too bad for a three day forecast.

Fits Me

Miscellany March 21, 2013

For the third straight morning skies have been dreary here in Tucson, with thick, high overcast and visibly dirty air. This morning there has even been some very high-level virga passing by - view above is from 8 am.

Re previous post - the new NAM 48-hour forecast this morning has a markedly different forecast for Saturday morning over Tennessee. Appears that the forecast MCS was a model hallucination, but will watch to see what evolves for Saturday.

This weekend is the first of the month-long Cherry Blossom Festival in Washington D.C. - see nice photo below. Looks like it will be a cold and wet and wintry weekend to kick-off this year's events.

David Blanchard has some beautiful photos of the comet PanSTARRS posted on his blog. One is below - link to his blog is at the right.

A Look East To The Tennessee Valley

The morning run of the NWS NAM forecast model this morning is very interesting, and it appears that an interesting forecast situation is developing over the Tennessee Valley for Friday night and Saturday morning (March 22nd and 23rd). The 72-hour forecast for 500 mb is shown above, valid 12 UTC 23 March. Not much exciting there, with strongest vorticity advection over Colorado and Nebraska and a ridge from the Gulf of Mexico to the Great Lakes. However, the same forecast for 700 mb (below) is very interesting, with an area of strong upward motion forecast to be centered on Tennessee.

The forecast for 850 mb (above) indicates a region of strong warm advection from northern Arkansas eastward across Tennessee. Forecast precipitation for the 3-hours ending at 12 UTC on the 23rd (below) indicates maximum precipitation centered near Nashville.

Finally the NAM forecast of simulated radar echoes (above) indicates an MCS over Tennessee, with strongest convective storms again near Nashville. So, the model forecasts a distinct, nocturnal and early morning MCS, with the vertical motion maximum produced both by meso-convection and low-level warm advection. Back in the late 1970s and 1980s, when the NWS was working hard to improve forecasts of heavy rain and flash floods, this was the type event that the models of that day could not forecast well. I'll keep an eye on how this situation evolves and report further. I do note that the forecast shown above also forecasts a nearly straight line hodograph, above a cool stable surface layer, with very strong wind speeds - a situation conducive to derechoes, if significant CAPE actually develops.

The situation becomes even more interesting in light of the latest NWS forecast for Nashville:

Note that snow is forecast Thursday night and Friday morning, with no thunderstorms until Saturday night.All-in-all, a very complex forecast, and I doubt that the model will get the details correct 3-days out.

Bats Have Returned

Our resident Western Pipistrella bats have returned to spend the summer hunting insects from the sanctuary of our front porch roof. They seem to be about two weeks early this year.

There is a serious explosion of Penstemons underway this year in our yard. However, a year ago today a heavy thunderstorm with graupel was pounding away at the flowers. Nothing like that this year.

Another Look At Long-Term

I took another look at the long-term GFS forecasts from the operational version of the model this morning. The forecasts were from 00 UTC last evening. The above is the forecast for total precipitation through the coming week. Much of the Southwest continues high and dry in the forecasts. I looked on out through the forecasts all the way to Easter Sunday (March 31st this year). Still no precipitation forecast for southern Arizona. Looks like the weather has gone on an extended Spring Break for us. Last March we had only one storm event, but that one brought 0.66", much better than this March's single storm so far.