HMT discussion for Mon/19 Mar
Nothing very persuasive among the observations or operational models this morning to think this system will be more than what was discussed yesterday. A few things remain that make it possible there could be more than an inch in some areas, most notably that, 1) the operational models all show more precipitation a mere 70 miles to the now of the HMT area, some over an inch, and 2) our 3 km runs all generate more precipitation (both ~70 miles to the nw with over 2 inches, and over the HMT area, with locally over an inch), and 3) there is a period of pretty decent orographic sw flow on Tuesday. Not sure how well the local models have been verifying on these max amounts, but there is up to 40 knots of sw flow at 700 mb for awhile on Tue ahead of the trough, before the winds shift to nw and weaken by 00z/Wed. Otherwise, the trend in the models has been towards more southern energy which is slowing things down even somewhat more, so most indications are that good precipitation would not start in the area until closer to 12z/Tue, with most but not all done by 00z/Wed, as showers linger to about 06z/Wed. The OAK RAOB this morning does not have a lot of moisture even though it is now into the intial lead plume, so this plume certainly has weakened a lot. SSMI imagery earlier this morning shows a couple of narrow portions exceeding 2 cm lurking offshore, however. HPC and the Sacramento WFO have both lowered their precipitation forecasts to under .75 inches max in the Blue Canyon area. The 09z SREF is generally in the .25-.5 inch range in the mean, with most members not far from this. So all in all still marginal, but still some chance (based on the 2 points above and the period of good 700 mb flow) that still could generate interesting precipitation amounts in the higher terrain.
Looking ahead, the trend with more southern energy is reflected now in the models diving the southern portion of this system to Baja and then the question is how long before it ejects to the northeast. This could affect the next system that was scheduled for this weekend, riding the strong Pacific jet stream of this week. This jet stream that has come out of Asia is quite impressive, forecast to be around 200 kts at 250 mb by later today. In fact, by 18z Tue the 12z GFS has an elongated 200 plus kt core from ~145 to 165E near 35N. The jet is forecast to weaken by the end of the week as it reaches the eastern Pacific but will carry a nice wave with it that now is predicted to wait until after the weekend to potentially affect the HMT area, perhaps this delay owing to the slow movement of the closed low that develops over the Southwest this week. Certainly a lot of uncertainty in all this, but the 12z GFS now forecasts a pretty moist system for the Monday/Tue timeframe (26-27 Mar) with ~1.5 inches in the GFS in the HMT area. This is followed by another potential storm towards the end of the week (Thu-Fri/29-30 Mar) and then another the following week. The EMCWF 00z run is consistent with the 12z GFS solution through the end of next week, as is last night's 00z GFS. Additionally, a number of members of the 12z GFS ensemble are in agreement especially with the system early in the week but also for something later in the week.
ed szoke NOAA/GSD