Thursday, May 12, 2016

Higher Moisture To East and To South

Before the next 500 mb short wave affects the Southwest this weekend, there is a period of southerly flow from low latitudes that advects higher moisture into southeast Arizona. Cooler and moist air is also trying to move westward from southern New Mexico and the Big Bend country. So, there is a bit of an interesting situation developing. I took a look at the 06 UTC WRF-NAM forecasts on the 5.4 km grid this morning (the WRF-GFS is running a bit late).

Above is the forecast for precipitable water (PW) valid at 6:00 am MST this morning - of most interest is the higher PW over the southern GoC. The model forecasts a surge-like northward push of higher PW that reaches to northern Sonora by 6:00 am tomorrow morning (just below). The higher PW air moves into southern Arizona by 6:00 am on Saturday the 14th (second below). The moisture from the east fizzles out along the Continental Divide and never makes it into Arizona in the model forecasts.

However, the northward push of lower-latitude moisture is quite impressive, especially around 700 mb - forecast below is for 700 mb RH valid at 9:00 am tomorrow morning. The WFR-NAM actually forecasts some thunderstorms near the border and light showers over parts of southeastern Arizona. So it is possible that we'll have a brief threat for dry thunderstorms along the Borderlands tomorrow afternoon - this would be the first such setup of the early summer and will be something to keep an eye on.

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