SWOMCD
SPC MCD 282345
MTZ000-290245-
MESOSCALE DISCUSSION 0620
NWS STORM PREDICTION CENTER NORMAN OK
0645 PM CDT TUE APR 28 2009
AREAS AFFECTED...ERN SLOPES OF CONTINENTAL DIVIDE OVER NWRN/NRN MT
CONCERNING...HEAVY SNOW
VALID 282345Z - 290245Z
SNOW FALL RATES OF 1-2 IN/HR ARE POSSIBLE OVER THE ERN SLOPES OF THE
CONTINENTAL DIVIDE IN NWRN/NRN MT DURING THE NIGHT.
WV IMAGERY AND UPR AIR OBSERVATIONS SHOW A LARGE SCALE TROUGH
POSITIONED OVER THE PAC NW. SEVERAL IMPULSES ARE ROTATING E-NE
AROUND THE TROUGH...ONE WHICH IS MOVING N THROUGH MT CURRENTLY...AND
ANOTHER WHICH IS POISED TO ENTER SRN MT DURING THE NIGHT. THE NRN MT
TROUGH IS FORECAST TO BE ACCOMPANIED BY AN INCREASE IN PRECIPITATION
RATES DURING THE NIGHT...WHICH WILL BE ENHANCED FURTHER BY
STRONG/SUSTAINED ELY UPSLOPE FLOW /WHICH IS RESULTING IN COLD AIR
DAMMING AND BARRIER JET DEVELOPMENT/.
SHORT TERM MODEL GUIDANCE INDICATE HEAVIEST SNOWFALL WILL TEND TO
SHIFT NWD DURING THE NIGHT WITH THE PROGRESSIVE UPR LVL
IMPULSE...WITH A POSSIBLE INCREASE IN SNOW FALL RATES /UP TO 2 IN
PER HR/ AS ELY LOW LVL JET EXPERIENCES FURTHER STRENGTHENING. IN
ADDITION TO HEAVY SNOW...STRENGTHENING SURFACE PRESSURE GRADIENT
ASSOCIATED WITH COLD AIR DAMMING WILL RESULT IN STRONG SURFACE
WINDS. GUSTS UP TO 40 KT APPEAR POSSIBLE AS WELL...DUE TO FAVORABLY
STEEP LOW LVL LAPSE RATES COMBINED WITH THE PRESENCE OF STRONG NLY
BARRIER JET JUST ABOVE THE SURFACE. CONSIDERABLE BLOWING SNOW AND
BLIZZARD LIKE CONDITIONS MAY BE POSSIBLE AS A RESULT.
..GARNER.. 04/28/2009
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...TFX...MSO...
LAT...LON 47271243 47551297 48261348 48921364 49121270 49091153
48571032 47851052 47331156 47271243
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