Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Junction Colorado
541 am MDT Thursday Jul 30 2015

Short term...(today through friday)
issued at 348 am MDT Thursday Jul 30 2015

The subtropical ridge that was centered over North Texas on
Wednesday continues to amplify into Colorado today. The west to
East Ridge axis is oriented roughly along Highway 50. Deep
monsoonal moisture will continue to invade south of the ridge
axis today and tonight. The SW Colorado valleys and SW San Juans will
see scattered showers and isolated storms forming through the
morning. By afternoon thunderstorm coverage increases. Storm
motion will be very slow...even stationary this afternoon and
evening. Precipitable water values climb to over 1.3 inches in The
Four Corners by late afternoon. This threatens locally heavy
rainfall mainly from Red Mountain Pass to Slumgullion Pass southward.
North of Highway 50 hot and dry conditions will continue adding a
few degrees to the afternoon high temperatures. Widespread showers
over the San Juans can often produce gusty winds into the west
Central Valley including the I-70 corridor. But light west
gradient winds aloft may limit these stronger winds. Southern
showers and storms are expected to continue through the tonight.

Friday the moisture across the southern zones diminishes somewhat.
So storm coverage may also shrink somewhat. Isolated to scattered
afternoon storms may form up to the I-70 corridor. Hot and dry
continues over the northern half of the forecast area.

Long term...(friday night through wednesday)
issued at 348 am MDT Thursday Jul 30 2015

Stable long wave pattern with high pressure centered over the southwestern
Continental U.S. Will prevail through the long term period. Monsoonal
moisture will circulate around the high center...diurnal heating
and periodic disturbances will be the primary mechanisms for
showers and thunderstorms. The deepest moisture covers the
southern half and this area stands the best chance of
showers/storms each day.

The GFS and European model (ecmwf) do indicate an embedded disturbance in the light
flow pattern that should enhance showers/storms across Utah and
Colorado. Neither agree on the exact day (either Sunday or monday)
nor intensity. Will see how this evolves and boost probability of precipitation when
confidence rises.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 541 am MDT Thursday Jul 30 2015

Thunderstorms and rain/rain showers will develop over the SW Colorado mountains after 18z
this afternoon and persist into the evening. Storms will expand
toward the SW Colorado valleys and into southeast Utah. Mountain ceilings may
fall below ils breakpoints from passing showers/storms. Isolated
-shra/-tsra may continue across this region through 12z Friday

North of the southern mountains...dry and stable regime expected
through the forecast period.


Gjt watches/warnings/advisories...


Short term...Joe

National Weather Service Glossary of Abbreviations