Monday, December 17, 2018

Still Looking Ahead

Have just looked at campus webcam images for past week - most of week was similar to above from 3:00 pm MST yesterday - cloudy to mostly cloudy. There were two days mid-week that were sunny to partly sunny.

Of interest is that light showers occurred across parts of metro after dark last evening - just a sprinkle here with a Trace, and no reports of 0.04" in the ALERT network.

The GEFS forecasts for Christmas Eve at 5:00 pm continue to have a large spread - I picked out 4 interesting members (500 mb above and surface with precipitation below). Some members of the ensemble forecast a closed 500 mb low somewhere over the Southwest/northwest Mexico. At the same time 2 of the members forecast precipitation over southeast Arizona at that time. The operational ECWF for same time is not much like any of GEFS forecasts. This is mainly because the European model is slower and forecasts a strong, closed low over our area after 192-hours. 

Saturday, December 15, 2018

Miscellany At Mid-Month

Another day begins with widespread cloudiness - as per Kitt Peak view to north at 6:51 am MST this morning. The IR satellite image below is from 13 UTC (6:00 am local) - note the wide plume of clouds from subtropics that covers most of Arizona.

We reached mid-month with only one precipitation event, and there's little on the horizon for the Southwest. Graphic above shows total precipitation forecast from the 00 UTC WRF-GFS on 5.4 km grid for period ending at 5:00 pm on December 22nd.

The East continues to have the corner on the big storm market, as an unusually warm system moves northeastward from Tennessee - surface plot below (from NCAR) shows rain from Florida northward past D.C.. Temperatures are above freezing from Florida to New York, which I think is fairly rare for this time of year.

Friday, December 14, 2018

Frosty Morning 14 December - Congratulations Al Roker

First - cold morning here at house with low of 25 F - some moderate frost around, and first morning of Fall/Winter with temperatures here in north part of the city down in the 20s. Both the airport and DM came in with lows of only 35 F, but nearby RAWS sites were cold also - Empire was 25 F and Sasabe was 21 F.

Looking far ahead, graphic above shows GEFS mean 500 mb and spaghetti plot out at 276-hours, which is 12 UTC Christmas morning. Mean keeps strong trough in east and  ridge off west coast. Of course at that long range, there is  also a huge helping of spaghetti on the plate.

This morning Al Roker is celebrating 40 years of doing the weather-cast on NBC - so kudos to Al!

Monday, December 10, 2018

Chilly And Dreary Morning

Visible image above from a bit before 9:00 am MST shows the high overcast that covers southern Arizona this morning (as per view north from campus a bit after 9:00 am at bottom).

Before the clouds moved in, the temperature here dropped to 34 F and cold air along Rillito is keeping the easterly winds that have been observed at airport aloft in this part of city.

Low yesterday was 36 F and on both mornings there was light frost on grassy areas at the park down right by the wash.

Saturday, December 08, 2018

Moderately Wet Event Here Moves Eastward

Our first precipitation event of December occurred on both the 6th and 7th, with two episodes about 12-hours apart. The ALERT maps here cover the entire event. Looks like total amounts about equally split above and below half an inch, with max amounts around three quarters of an inch. Considerable lightning and thunder occurred during both episodes, but was much more widespread in the second, heavier episode yesterday. Map second below covers entire event and shows CG flash density (from and Vaisala).

The airport had 0.72", considerably exceeding yesterday's model forecasts - including all the GEFS plumes. Here at house the total was 0.58" - nice event to start December with amounts more than November's one event by more than two.

The long-range is fairly uncertain - a weak system passes by around December 12th, with little precipitation forecast to accompany it. By 240-hours (5:00 pm MST on December 17th) there is a very large difference between the operational GFS (above) and ECMWF (below) forecasts. last time I did a long-range comparison the average of the two models was closest to observations - this time?

Friday, December 07, 2018

Widespread But Light Rains Lat Night

View from Kitt Peak looking south this morning shows fog in valleys to east and west, as well as a skinny Cb far to the south. Down at bottom is deer caught in fog from webcam near Summerhaven.

Rainfall last night across metro was generally about a tenth of an inch - heavier amounts occurred west to north of Catalinas - no reports of half an inch or more. Only 0.09" here at house between 6:00 and 09:00 pm MST. ALERT map above is for 24-h ending at 6:30 am. Flash density map for CGs (below from and Vaisala for 24-h ending at 5:45 am) indicates some thunderstorms from southern New Mexico west to around San Diego and south into Mexico - there were reports of thunder around the metro last evening.

Highest PW amounts have remained south of 30 degrees north, as per MIMIC TPW analysis for 5:00 am above. The forecast below is from the 06 UTC WRF-NAM forecast run and shows total precipitation forecast through 5:00 pm tomorrow afternoon. The GEFS QPF plumes from the same time indicate possible rain amounts at airport ranging from 0.22" to 0.54" for today, as 500 mb short waves moves our way. The WRF NAM forecast is near the GEFS average of 0.35" for airport.

Thursday, December 06, 2018

Update On First December Weather Event

Above is 13 UTC MIMIC analysis of total PW this morning. Center of circulation is now west of San Diego with no well-defined atmospheric river. The wild card for us may be the northward-moving plume of higher PW that has been coming northward up the GoC and Sonora. Current loops seem to indicate that this stream may stay off to our east; however, radar indicates a large area of precipitation already over the northern GoC. Considerable uncertainty as this event gets underway.

The NAM 500 mb forecast this morning for 12 UTC tomorrow morning is below. The short wave is just moving across southern California at that time. Analysis shows that the flow splits west of Oregon, with strong northerly and southerly branches,

The 06 UTC GEFS plumes forecast (bottom) more rain at airport than yesterday, with a spread from 0.30" to 1.00" at airport, and average of 0.55". The 06 UTC WRF forecasts are now much drier than any of the GFS forecasts, with only about a tenth of an inch at airport. The forecast soundings do indicate a chance for thunderstorms both this evening and again tomorrow morning.