Monday, March 28, 2016

Last Gasp For March 2016

A large and cold closed-low at 500 mb is digging southward this morning from the Northwest, following a mostly overland track. The 500 mb analysis above is from the 12 UTC NAM this morning and shows a kidney-bean shaped low with circulation centers over the northwest corner of California and over northern Idaho. The models continue to forecast this low to remain elongated, with a positive tilt, that eventually leaves behind a separate but weaker system over the Southwest.

The main impact from the large, initial system will be winds and dust - as per the current morning forecast from the NWS for the airport (above). Note that there is a Red Flag warning in effect for southeastern Arizona - as usual ignore the warning area shown on the NWS Homepage and click on Hazards if you want to see the actual area being warned. Below is Atmo's WRF-GFS forecast from 06 UTC for 10-m winds (in knots) valid at 2:00 pm MST this afternoon. Note that 24 kt equals 28 mph.

The GEFS forecast plumes for TUS are essentially mirrored by the NWS forecast shown above. The QPF plumes from the 06 UTC forecasts (above) indicate an anemic system (as per other systems last several months). Most members forecast a slight chance for up to 0.02" at the airport, with a few members being slightly more optimistic - timing of shower possibilities within the ensemble is all over the place. The plumes for 10-m wind speeds (directly below) forecast the next two afternoons to be windy. The temperature plumes (second below) indicate a fairly strong frontal passage sometime tomorrow morning, with afternoon highs about 20 F or so colder than those forecast for today.

Finally, the GEFS average 500 mb height forecast below is for 5:00 pm MST on Wednesday the 30th. The portion of the system hanging back over the Southwest seems to have some possibility to pick up a bit more moisture, due to longer fetches over the ocean - so it will be interesting to watch how the PW evolves between here and Hawaii late Tuesday and Wednesday.

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