Monday, September 19, 2016

Low-Level Moisture Surges Rapidly Northward Up GoC

Paine has become a weak hurricane as it moves northward this morning. The current track forecast from NHC is shown above - NHC now forecasts the low-level circulation to make it a bit further north before it dissipates around 30 degrees north. Yesterday's discussion regarding the mid-level circulations of Paine and the 500 mb to its north remain valid (see previous post).

Low-level moisture has surged rapidly northward up the GoC during the past 24-hours. The plot of detected CGs below is for 12-hours ending at 5:00 am MST this morning (from Atmo and Vaisala) - thunderstorms have developed far north of Paine and impacted the San Diego area already. Additionally, the surge has already reached Yuma where the dewpoint temperature jumped from 44F at 3:00 am to 72F at 6:00 am.

The two panels here show the MIMIC total PW analysis from CIMSS at Univ. of Wisconsin. Analysis above is for 11 UTC yesterday, the 18th, while below is for same time this morning on the 19th. The push of very high PW up the GoC is shown very clearly.

The blended PW analysis from CIRA at Colorado State is shown below - also for 11 UTC. The CIRA analysis indicates that the gradient of PW is very strong along the Borderlands and that very moist low-level air will likely be pushing into much of southern Arizona during this morning.

The two variants of the WRF model run at Atmo continue to forecast considerably different precipitation outcomes from the affects of Paine. I've looked at the 5.4 grid forecasts from 06 UTC last night. The forecast of accumulated rainfall through 5:00 am MST on the 21st (Wednesday morning) above is from the NAM version of the model, with heaviest precipitation occurring in a wide swath across much of Arizona. The GFS version (below) for the same period keeps heaviest rainfall far to west in southern California and the lower Coloradao River Basin. Of note is that the GFS version develops thunderstorms in our area, well east of the main Paine band of precipitation. 

So Paine remains a bit of a coin flip locally but is certainly providing a rapid change in our local weather conditions. Current radar data from Yuma and San Diego would seem to favor the WRF-GFS forecast below at this time. The best chance for thunderstorms in our area may occur late tonight and tomorrow morning, before very warm air from Paine moves overhead in the middle-levels.

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