Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Sun Apr 21 2019
Valid 00Z Mon Apr 22 2019 - 00Z Thu Apr 25 2019
...Central and Southern Rockies...
Upper trough evident on WV imagery this afternoon will slowly
amplify while dropping southward into the Great Basin. There is
strong model consensus that this feature will close off and
continue to sink southward into Northern Mexico Tuesday before
filling and opening into the Plains on Wednesday.
As this occurs, upper jet coupling is expected to develop between
a slowly retreating northern stream jet max and an amplifying
southern stream max wrapping around the upper low. Although
neither of these features are intense, the modest but prolonged
diffluence where the RRQ of the northern jet and LFQ of the
southern jet overlap will produce heavy snow from WY southward
through CO and into NM. Despite the presence of this upper trough,
snow levels will be high, and rise into early next week as broad
mid-level ridging tops the sinking low. At their minimum,
accumulating snow should be confined above 7000 ft Monday in WY,
and climb towards 10000 ft Wednesday as the low dissipates and
ridging becomes more dominant. This will bring an end to the
heaviest snow, which is likely only in the highest terrain Monday
On Monday, WPC probabilities for 8 inches are moderate in the Wind
Rivers, Uintas, and Colorado Rockies above 8000 ft. By Tuesday,
the heaviest snow axis shifts southward, and the heaviest snow of
the period is likely in the San Juans and Sangre De Cristos, where
moderate probabilities exist for 12 inches on day 2, with residual
light accumulations possible into day 3 but only in the highest
terrain above 10000 ft.
The probability of significant freezing rain is less than 10
percent Days 1-3.