Complicated weather pattern currently across the US. A large high pressure sits over the inter-mountain West, an elongated front extends from Texas northeast into the Great Lakes, and another cold front is sweeping south into the northern Plains.
Fire weather focus is for southwestern California, where breezy off-shore winds continue Wed/Thurs in response to diverging winds of the high pressure centered over northern Utah. Sustained winds along higher terrain are expected up to 20-25mph with gusts to 45-50 (see graphic below). With these downsloping winds, very dry/warm conditions are expected with RHs in the mid-to-upper single digits. In combination with ongoing drought conditions, this will create explosive fire weather conditions Wed afternoon and Red Flag Warnings are posted. Winds are expected to weaken Thurs as high pressure moves northward. However, some areas will still see aggravated fire weather conditions with gusts exceeding 20mph in southern CA. After Thurs, winds will be much calmer for the remainder of the period but conditions will remain very dry. Daytime RH isn’t expected to exceed 15% for the entire period with very poor overnight recoveries into the weekend.
San Diego NWS local forecast model depicting possible winds for 21z Wednesday.
Elsewhere, several cold fronts are expected to traverse the Plains and Eastern US through the period. With these frontal systems, quick periods of dry and/or windy conditions are possible. The first front is currently entering the northern Plains and will bring a period of windy conditions for central South Dakota with RH dropping to 20-25% Wed afternoon. Overnight Wed the front moves further southeast into the Mississippi Valley, reaching the Appalachians Thurs. Friday, it reaches the southeastern US and windy conditions move offshore. However, enhanced fire concerns exist with RHs ranging 20-25% from east Texas to northern Florida. Friday afternoon, another quick moving cold front enters the Plains with strong winds across the northern Plains. This second front will move eastward and repeats the process through Sunday.
A third, much stronger cold front moves south from Canada on Sunday evening. This front will bring much colder air to much of the central and eastern US early week. Very strong winds are possible with this front on Sunday/Monday in the central Plains both ahead and behind the cold front. Enhanced fire conditions are possible across the central Plains through this 48 hour period, especially for portions of eastern Colorado, Kansas, Nebraska, and Oklahoma.
Some rainfall is likely from these fronts, however, much of it will avoid the southeastern, central, and southwestern US. Image from NWS Weather Prediction Center – 5 day rain predicted rainfall total.
Southern CA: Red Flag Warnings for Wed, critical fire weather with strong winds (gusting to near 50mph) and very low RH (4-9%). Winds will weaken Thurs (gusting to 20mph), and become calm Fri-remaining very dry. Poor overnight RH recovery through the week, and into the weekend.
ND/SD: Enhanced fire weather conditions on Wed & Fri afternoon with strong northwest winds (gusting to 60mph) and low RH (20-25%).
TX/LA/MS/AL/GA/FL: Locally enhanced fire weather conditions on Fri-Sun afternoons with low RHs (25-35%).
Western KS, NE, OK/Eastern CO, WY: Beginning Sun morning and continuing until a cold front passage Monday afternoon, very windy conditions (gusting to 55mph) and low RHs (5-15% increasing Mon afternoon).