Last night it rained buckets at times in Northern California. However, that’s nothing. Here is this morning’s “area forecast discussion”:1 from NOAA for San Francisco.

bq.. We will get only a short break between storms as the next system is already approaching 140w and will begin spreading clouds and rain over at least the n bay as early as Tue pm. By wed it will spread substantial rain Thru our district again…lasting into wed night. The GFS indicates the wed system will probably be somewhat wetter and breezier than the current storm with a good 1-3 inches in the N Bay and significant rain in all areas of the district.

After another break on Thu we get set for the biggest storm of the week beginning on Fri. The GFS and Euro bring in heavy rain and wind to the entire district Fri/Fri night and this is when our main flooding concerns will kick in. The models are consistent in forecasting a very strong diffluent jet over our area with copious subtropical moisture and a good deal of wind. Current model timing is for the heavy rain to move into the N Bay during the day Fri and spread over the rest of the district late Fri aftn thru the night. This storm looks easily capable of producing 2-6 inches of rain in most areas of the district in the 24 hour period Fri/Fri night with locally heavier amounts in the hills. This is almost certain to cause flooding in the N Bay…probably in the Santa Cruz mtns…and possibly just about anywhere else in our region.

p. Yeah, you sometimes need a translator to understand what they are saying. The GFS and Euro are numerical weather models used in forecasting. A diffluent jet means the jetstream is spreading out which supports low pressure and atmospheric instability (ie, precipitation).

A great site for checking on the near-term precipitation forecast is NOAA’s “Hydrometeorological Prediction Center”:2. A usefully subpage from this site is an aggregation of the quantitative precipitation forecasts, which you can find “here”:3. For example, here’s an image of the five day quantitative precipitation forecast (QPF).

You’ll notice that the amount of rain increases rapidly as you move up the California coast. This is typical of winter storm systems where it might be completely dry south of Monterey, while raining buckets up the north coast.

[3(HPC - Quantitative Precipitation Forecasts)]http://www.hpc.ncep.noaa.gov/qpf/day1-5.shtml

[2(Hydrometeorological Prediction Center homepage)]http://www.hpc.ncep.noaa.gov/

[1(NOAA area forecast discussion for San Francisco)]http://www.srh.noaa.gov/fwd/productviewnation.php?pil=MTRAFDMTR&version=0