2006-03-01 WX Discussion and Forecast
The weather discussion today will look at the next system that begins later this week and then will attempt to describe the longer range picture for next week and possibly beyond.
Both NAM and GFS are fairly parallel on this next system however the GFS wants to keep the closed low together longer as it moves inland with the NAM opening it up earlier (9z 3/3) and bringing it in as a progressive wave, the GFS holds off on this and finally opens the wave at 00z 3/4. Neither model has a true surface fropa wind signature with this system however both indicate a weak upper level trof passage at about the same time between 21z 3/3 and 00z 3/4. The NAM has this as a stronger feature and like yesterday this corresponds with a drop in the precip intensity. Actually, in the NAM it looks like it might spell the end of the event. The GFS continues precipitation beyond this time. Both models have the start of this event at about 06z 3/2 with the precipitation on shore but not quite to the ARB at 03z 3/2. The precipitation in both models begins light with an early maximum around 12-15z 3/2. The precip in the NAM drops abruptly when the winds back to the SE between 21z 3/2 and 3z 3/3. QPF amounts for this system between the models is again pretty consistent like they were yesterday. The NAM has a mid-storm total eq liq. of 1.22 inches by 18z 3/2 before the lull and then continues through to 21z 3/3 with an ending storm total at that point of 2.06 with 0.84 falling in the latter half of the event between 3z 3/3 and 00z 3/4 when then NAM has the event ending.
The GFS continues precipitating a bit longer but with comparable QPF for the event of 2.09 inches ending by 12z 3/4.
Winds from the NAM show less than optimal direction throughout, with primarily south wind direction (as also progged yesterday) with speeds between 10-30 knots. It is only at the end of the event that winds veer to the SW for a brief time. This occurs at 12z 3/3 and 00z 3/4 and coincides with GFS precip rate of about a quarter inch per six hour period, of course the NAM is ending the event at about this time also.
The thermal profile appears to again be much warmer than progged last week, but maybe a tad cooler than yesterday near the end of the event. The freezing level starts at about 850 hPa and after 09z 3/2 begins falling in elevation, finally reaching abut 900 hPa at 15z 3/3, after that time it climbs back to 850 by 00z 3/5.
Looking at the ensembles for additional guidance on the end of this system and the following events it appears that the GFS ensembles are all dry by 09z 3/4. The normal GFS run has the next system beginning about 6z 3/6 (Monday). The GFS ensembles have the system well underway (about 100% agreement) by 12z 3/6 and the ensembles keep this going until 12z 3/8 (Wednesday) and there appears to actually be a surface fropa in the normal GFS run that occurs about 00z 3/8 which probably coincides with the event end, but the timing of course is the issue, putting all of this together, it could be any time between 00 and 12z on Wednesday.
Moisture plumes are looking a bit anemic in the future. The last vestige of a good tropical fetch is now departing the CONUS well south of the ARB and was associated with the last IOP. There is a minor surge from the NW 06z 3/2 associated with this event of about 2.0cm and then the next plume arrives at about 06z 3/6 and is very narrow extending back to a major N-S oriented plume at about 175w. This mid-pacific plume has 4.9cm of water to about 30N and then it falls off to about 3cm up to 40N. An appendage from the top part of this plume finally shears off and interacts with the ARB around 18h 3/9 (Thursday) with pw values of 2.8cm. After this episode, plumes really don't show much promise of making it to the ARB until 06z 3/16 (Thursday) about one week later.
Dan Birkenheuer - ESRL/GSD