April 27, 2021 – Dry and much warmer weather returns today and continues through the week.
Discussion
Upper low pressure over NV and CA forecast to consolidate as a minus 4 anomaly 5H upper low over the CA/AZ/Mex later today. Main impact will be warming temps and the development of modestly breezy, but dry, Nly winds as high pressure builds in behind the low.
Downward momentum transfer of winds aloft indicates wind gusts up to 18-25 kts in the Valley later today with min RHs lowering to around 10% mainly along/W of I-5 this afternoon. As 5H heights recover, 850 mbs temps and low to mid thickness values suggest max temps today will be some 12 degrees or so warmer than yesterday. Highs in the upper 70s to around 80 forecast for the Valley, mostly 50s and 60s elsewhere. Vort max near the ID/NV border may trigger isolated showers over our Srn Zone 60 near the Crest as it retrogrades towards the LA area by this evening.
Warming trend continues for the rest of the week with the warmest day expected on Thu as the Ern Pacific ridge shifts inland. 850 mbs temps warm into the mid teens deg C with max temps nearing 90 in the Valley, some 13-14 degrees above normal. (NBM Viewer shows a 43% chance of 90 at DTS, 27% for KRDD, 22% for KSCK.)
An increase in cloud cover on Fri associated with an approaching short wave trof moving into the Pac NW on Sat may limit max temps a couple of degrees on Fri, followed by onshore flow and minor synoptic cooling Sat.
Extended discussion (Saturday through Tuesday)
EPAC upper ridge remains dominant synoptic feature through the extended forecast period. Ridge weakens over the weekend as short wave trough moves through the West Coast. Main effect will be a minor cooling trend, however high temperatures remain about 10 to 15 degrees above normal through the weekend. Temperatures trend up again early next week with some locally gusty north to east wind as upper ridge rebuilds.