NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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604
FXUS66 KSTO 241210
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
410 AM PST Sat Feb 24 2018


.SYNOPSIS  
Below normal temperatures will continue. Snow showers possible over the mountains today with additional systems next week bringing more widespread precipitation.
.DISCUSSION  Next system now moving south from Vancouver Island and Puget Sound will not be impactful for Norcal today as it will be a weak, rather benign (nuisance) wx system bringing some light showers to mainly the mountains. Some high clouds are already moving southward across interior NorCal, but these are not having much effect on temperatures as current readings are colder through much of the valley with only the thermal belts seeing milder temperatures. Dry weather on Sun will be followed by another wx system on Mon. This system will also be similar to its predecessors, cold with relatively low QPF, and high snow ratios. (Favoring the NBM snow ratios during these colder GOA systems.) However, the Central Valley should see more rainfall than yesterday`s system. NAM Bufkit forecasts around a quarter inch for SAC, and this may be the last shot of rain this month. DTS rainfall for the month remains at zero through today, although SAC Exec had .01" yesterday. Here is the list for the driest Febs for DTS: 1) 0.04 in 1899 2) 0.16 in 1913 3) 0.19 in 1995 4) 0.21 in 1953 5) 0.26 in 1997 & 2013 SPC plume forecasts show about 10 inches of snow for the mean at BLU for the Mon system, and our forecast is trending toward that average, and about 15-20:1 snow ratios for the Sierra. (The "normal" SLR is about 9:1.) A wide swath of 8-12 inches of snow is forecast with isolated amounts greater than a foot near the Sierra Crest. The WR US West Coast AR Landfall tool (Probability of IVT) continues to show a lack of moisture, albeit it is not as "bone dry" for the next 16 days as yesterday`s models. However, there remains a lack of significant ARs. What moisture there is will be spilling over the Pac Ridge and basically eroding as it hits the Pac NW and spreads inland into our CWA. (One could make a weak argument that the Mon system may have a little more moisture than what was forecast yesterday.)   Another break Tuesday with breezy north winds ahead of more active weather likely to return for early March.
.EXTENDED DISCUSSION  (Wednesday THROUGH Saturday)  A period of dry weather is expected for the beginning of the forecast period except for shower activity over the mountains. Then, a deepening trough and its associated frontal boundary will impact the area late Wednesday into the early weekend. However, forecast models are still struggling with the progression of this system and precipitation amounts. Regardless, this system will likely bring widespread precipitation across interior NorCal. Early QPF estimates suggest 0.25-1" across the Valley and 1-2.5" over the mountains through early Friday, though amounts will likely change this far out. In addition, periods of heavy snow could cause travel difficulties over the Sierra. Breezy to gusty winds are expected as the system moves through, especially over the Sierra. Temperatures will remain below seasonal normals.
.AVIATION 
VFR conditions next 24 hours except local MVFR conditions over the mountains due to scattered snow showers after 15z Saturday. Winds less than 12 kts at TAF sites except for gusts up to 20 kts from KRBL northward after 18z Saturday.
.STO   WATCHES/WARNINGS/ADVISORIES    
None.   

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