Area forecast discussion
National Weather Service Salt Lake City Utah
245 am MDT Wednesday Aug 28 2013
Synopsis...temperatures will warm with a ridge of high pressure
building into the region. However plenty of moisture will keep the
threat of daily isolated to scattered showers and thunderstorms.
&&
Discussion...water vapor loop shows a ridge over the central Continental U.S.
And a trough off the Pacific coast. Several disturbances are
rounding the ridge from the Gulf of Mexico and northern Mexico
toward The Four Corners. Acars 400-250mb wind observations place a
75-105kt southwesterly jet from central California into the northern
rockies. Rap...GOES...GPS sensors...and 00z slc radiosonde observation indicate
precipitable water values range from 0.70"-1.55".
As the central Continental U.S. Ridge tries to build westward...subtle drying
and warming will gradually take place from east to west. While the
column dries a bit especially east...surface dewpoints are still
well into the 50s most valleys. Enough moisture will remain in place
to support more traditional diurnal convection during the next
several days initiating on the higher terrain. Locally heavy
rainfall is still a threat.
Global models indicate a series of disturbances with origins over
the Gulf of Mexico will round the broad central Continental U.S. Ridge and
impact the Great Basin next weekend. The combination of moisture
transport and these disturbances should yield better coverage for
convection. However...both GFS and European indicate in 850-500mb
streamlines/specific humidity fields that a drier northerly flow may
be present near the Idaho border. So ended up increasing probability of precipitation 10%
across southern Utah and lowering 10% near Idaho this weekend.
GFS now on board with European maintaining another surge in moisture
by the middle of next week as the ridge once again propagates to our
east opening up a more southerly flow. No changes in scattered pop
distribution yet.
I suspect we're looking better for a chance of XC flying over the next few days, with today being more of a transition day in terms of percip and TS potential.
Expect the unexpected. We have plenty of potential for TS and the clear skies will help keep the day active with deep cumulus clouds. Some will be threatening, some will only look scary--I for one will err on the conservative side rather than roll the dice to find out, so be careful and watchful.
Winds are SSW, with light southerly flow in the valleys and maybe 12 mph around 14,000 ft, which will likely be about cloud base for the day. Temps will rebound, but bring warmer clothes for flying, as 14k is around 40 F today.
UPDATE: Models seems to disagree with winds aloft today, as do the official aloft forecast for SLC from the NWS. We could see as much as 16mph near 14,000 feet today. Real-time surface obs this morning near ridge top are showing as high as 15mph at 10,000 ft. This is compressed flow, so assume aloft is more like 10mph at 10k feet.
A MUCH drier air mass is overhead by mid day, according to the GFS, so this should help keep TS scattered over favorable locations in high terrain just as the NWS notes indicate.
Not sure what else to post. We'll brief in person on launch.
-CG
No comments:
Post a Comment