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HMT Forecast Discussion for Thursday 13 Mar 08 (entered 19z/Thu)

Actually had a burst of rain last night into the morning hours with the current disorganized system. Rain began according to the KBLU METAR at 0611z, and as of 16z the METAR site recorded 0.68" with a temperature of 40F/~4C. Interesting to compare this to the ESRL gages at BLU: 0.82" for the tipping bucket (TB) and 0.98" for the hot plate (HP). At Alta 0.55"/TB and 0.75"/HP, and at Big Bend 0.59"/TB and 0.63"/HP with a temperature there of 3.6C. Expect off and on generally light rain showers today but could see another 0.10" or so at KBLU (18z total on the KBLU METAR is 0.75"), then gradually turning cooler and would think things should go to snow late today or tonight. Some light precip on Friday will increase with the next wave but then temperatures will be considerably colder with snow off and on at KBLU Friday night into Sat night.

Looking farther ahead there is a system midweek of next week that is fairly weak with a decent moisture plume extending back to nw of Hawaii, but most of the moisture with it is currently forecast to hit north of the ARB in the Pacific NW, so barring a southward shift this system is not expected to do much. It seems a longshot that this system will amount to anything of interest except for the moisture plume, which if compared to today's system is actually predicted by the 12z/GFS to be even a little better. But little precip is actually forecast from the GFS for the ARB with this. This plume will be hitting the Pacific NW mon-tue (17-18 Mar) with some good precip forecast by the GFS. At upper levels at this time the upper low is in the Gulf of Alaska but a strong zonal jet extends to its south from the Pacific NW back to the WSW to near 35N/160W. The jet and moisture plume are forecast by the GFS to drift southward Tue-Wed with the plume gradually falls apart. The main chance then would be that more moisture is left in the plume when it finally drifts into the ARB region around Wed/19 Mar. It seems I recall something like this with a system way back in Dec/07 (?) that ended up having more moisture then expected when it eventually drifted into place, but was not IOP-worthy as it kept moving south. The other item of interest with the feature would be that the snow level would likely be high enough for rain at Blue Canyon. Not a lot of folks on the conference call today but considerable skepticism was expressed by HPC that this could amount to anything of interest. We certainly can watch it, as the next potential would not occur until the following weekend or maybe beyond.

This greater potential appears to lie in a major trough that deepens off the Pacific NW later in the week and brings considerable moisture into that region into the weekend of 22-23 March into the early part of the next week. How far south this goes is the uncertainty at this point and will probably have to be watched if this is of interest. The 12z deterministic GFS does bring some good precip into the area Sun-Mon/23-24 Mar but most of it is farther north. Ensemble set from 00z has overall good agreement on a strong system but variations in position of the plume of moisture/precip into CA and the Pacific NW. A look at the loop of the 12z/GFS on the U of HA site shows that the system for the weekend is a strong upper low that does not have a good moisture tap into higher PW areas. In fact it is not until after this system that one by midweek of the following week (~Wed/26 Mar) that a system comes in on more zonal flow with a much better moisture tap, though in the longer range models remains a fast-mover. It seems the best chance of some big event would be the strong wave for next weekend (22-23 Mar) coming in farther south and tapping into more moisture than it is currently forecast to do. Currently a few members of the 00z GFS and Canadian Global ensembles (the NAEFS) have such a scenario, but not a majority. The latest 12z GFS ensembles paint roughly the same picture, with little chance for the system mid next week but some members quite favorable for the following weekend and beyond. It appears from the telcon that all of this would be too late in the game to be of interest for an IOP, with the current last date of 21 Mar.

ed szoke NOAA/GSD/CIRA