Severe Thunderstorm Warning 20, NWS Elko, NV

NORTHERN GREAT BASIN FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ELKO NV
212 PM PDT THU JUL 25 2002

.SYNOPSIS...WEAK LOW PRESSURE WILL MOVE ACROSS NORTHERN NEVADA THIS
EVENING...PUSHING SHOWERS AND THUNDERSTORMS FROM EAST CENTRAL AND
EXTREME EASTERN NEVADA INTO UTAH BY MIDNIGHT. HIGH PRESSURE IN THE
EASTERN PACIFIC WILL MOVE EASTWARD ACROSS THE GREAT BASIN SUNDAY
THROUGH THURSDAY PROVIDING A PERIOD OF DRY WEATHER.

.DISCUSSION...GOES PRECIPITABLE WATER SHOWS DRIER AIR MOVING IN
FROM THE WEST ACROSS CENTRAL PORTIONS OF NV THIS AFTERNOON.
THUNDERSTORMS PRODUCING HEAVY RAIN...STRONG WIND GUSTS AND LARGE
HAIL HAVE DEVELOPED IN THE RELATIVELY MOIST AIR MASS ACROSS
SOUTHERN EUREKA COUNTY AND WHITE PINE COUNTY...AS THE LEFT FRONT
QUAD OF THE 3H JET HAS MOVED ACROSS CENTRAL NEVADA THIS AFTERNOON.
COMPARISON OF THE 12Z AVN RUN...OR ACTUALLY THE SUBSTITUTED NOGAPS
RUN...ON THE POSITION OF THE VORTMAX IN SOUTHERN OR...ASSOCIATED WITH
A 5H TROUGH PROGRESSING EASTWARD ACROSS OR...REVEALED THAT THE 18Z
POSITION OF THE VORTMAX ON THE AVN RUN WAS FARTHER SOUTH THAN THE
POSITION OF THE VORTMAX ON WATER VAPOR. PREFER A MORE NORTHERLY
TRACK OF THIS VORTMAX ACROSS THE EXTREME NORTHERN TIER OF NV THIS
EVENING. HAVE RETAINED ISOLATED POPS FOR CONVECTION ACROSS NORTHERN
ELKO COUNTY...ESPECIALLY THE EASTERN HALF...AS THIS VORT FEATURE
MAY PROVIDE ENOUGH DYNAMICS TO SET OFF CONVECTIVE ACTIVITY. ONCE THE
TROUGH AXIS MOVES THROUGH EASTERN NV DURING THE MIDDLE OF THE
EVENING...THE DRIER AIR FROM THE WEST WILL MOVE IN QUICKLY. SHOWER
AND THUNDERSTORM ACTIVITY SHOULD LAST THE LONGEST IN WHITE PINE AND
EASTERN ELKO COUNTIES...WHERE THE PW VALUES HAVE BEEN HIGHEST...
NEAR 1.00 INCH...AND MOISTURE WILL BE SCOURED OUT LATER THAN IN THE
STRONGER WEST TO NORTHWEST FLOW TO THE NORTH. DRY SLOT OF AIR
MOVING ACROSS CENTRAL CA INTO WESTERN AND CENTRAL NV AT THIS TIME
WILL BRING CLEARING TO THE ENTIRE CWFA SHORTLY AFTER MIDNIGHT. RIDGE
IN THE EASTERN PAC WILL BUILD EASTWARD TOWARD THE WEST COAST FRIDAY
THROUGH SUNDAY...BRINGING A DRY AND COOLER FLOW OF NORTHWEST AIR
ALOFT TO THE REGION. HIGH TEMPERATURES WILL BE BELOW NORMAL THROUGH
THE PERIOD. THE RIDGE CONTINUES EASTWARD MONDAY THROUGH THURSDAY
AND SETS UP OVER THE GREAT BASIN BY TUESDAY. THIS WILL INITIATE A
WARMING TREND MONDAY THROUGH THURSDAY. THE BIG QUESTION TO BE
ANSWERED IN THE EXTENDED IS WHETHER OR NOT MOISTURE FROM THE
REMNANTS OF TROPICAL STORM DOUGLAS WILL BECOME ENTRAINED IN THE MID
AND UPPER LEVEL FLOW WEDNESDAY AND THURSDAY BETWEEN THE RIDGE IN
THE GREAT BASIN AND A TROUGH APPROACHING THE WEST COAST. MRF HAS
SHOWN THIS MOISTURE MOVING INTO THE GREAT BASIN. WILL LOOK TO THE
NEXT MODEL RUNS FOR BETTER GUIDANCE AND INCLUDE PARTLY CLOUDY IN
FORECAST CWFA-WIDE WEDNESDAY AND THURSDAY FOR NOW.

.EKO...NONE.

SMITH