NORTHERN ARIZONA FORECAST DISCUSSION
NWS FLAGSTAFF AZ
AFDFLG 230 PM MST TUE FEB 13 2001
SYNOPSIS...A STRONG AND MOIST PACIFIC STORM SYSTEM HAS BEGUN TO MOVE
ACROSS THE SOUTHWEST TOWARDS ARIZONA. SNOW WILL SPREAD FROM WEST TO
EAST ACROSS THE NORTHLAND THIS AFTERNOON AND TONIGHT WITH
SIGNIFICANT ACCUMULATIONS EXPECTED OVER THE HIGHER TERRAIN. SNOW
LEVELS WILL LOWER TO ABOUT 3500 FEET BY WEDNESDAY MORNING. THE COLD
AND UNSETTLED WEATHER WILL CONTINUE INTO THURSDAY. CLEARING SKIES
AND WARMER TEMPERATURES ARE EXPECTED ON FRIDAY AND CONTINUING INTO
THE WEEKEND.
DISCUSSION...CLOUDS ARE RAPIDLY INCREASING ACROSS MUCH OF NORTHERN
ARIZONA THIS AFTERNOON. SHOWERS ARE ALREADY OCCURRING OVER THE
HIGHER TERRAIN OF THE MOGOLLON RIM AND OVER MUCH OF YAVAPAI AND GILA
COUNTIES.
THE STORM HAS GONE THROUGH AN INTERESTING CYCLE OVERNIGHT WITH A
LARGE AREA OF ENHANCED CLOUD TOP WHICH HAS NOW DIMINISHED. THIS IS
IN RESPONSE TO THE JET STREAK THAT WAS ROUNDING THE BASE OF THE
TROUGH YESTERDAY MORNING AND HAS NOW EXITED THE REGION. ANOTHER JET
STREAK WAS OBSERVED IN THE ACARS DATA AND WILL ROUND THE BOTTOM OF
THE TROUGH OVERNIGHT AND SHOULD ENHANCE THE PCPN AGAIN AS IT MOVES
ACROSS AZ.
LOW LEVEL MOISTURE CONTINUES TO INCREASE AND DEWPOINTS ACROSS SRN AZ
HAVE JUMPED IN THE PAST FEW HOURS. AT THE SAME TIME, A MOIST PLUME
CAN BE SEEN ON SATELLITE IMAGERY BEGINNING TO MOVE ACROSS SW AZ.
OROGRAPHICS WILL REMAIN FAVORABLE THIS AFTERNOON AND TONIGHT WITH A
40+ KNOT FLOW AT 700 MB. THE COMBINATION OF JET DYNAMICS, UPSLOPE
FLOW, AND DEEP MOISTURE WILL COMBINE TO PRODUCE SIGNIFICANT AMOUNTS
OF SNOW OVER MUCH OF THE CWFA TONIGHT AND TOMORROW. SNOW LEVELS
SHOULD DROP TO 3500 FEET OVERNIGHT.
WILL CONVERT WINTER STORM WATCH INTO A HEAVY SNOW WARNING EXCEPT FOR
ZONES 4 AND 6 WILL DOWNGRADE TO A SNOW ADVISORY. WILL ADD ZONE 11
INTO THE SNOW ADVISORY.
EXTENDED...MRF AND ECMWF STILL SHOWING LARGE DIFFERENCES IN THE
DETAILS BUT THERE IS AGREEMENT IN THE GENERAL PATTERN TOWARDS A MORE
SEASONABLE PERIOD WITH PARTLY CLOUDY SKIES. WILL LUMP DAYS 3-7
TOGETHER WITH TEMPS NEAR CLIMO VALUES.
.FGZ...HEAVY SNOW WARNING TONIGHT AND WEDNESDAY FOR
ZNS...8...15...16...17...18...37...38
SNOW ADVISORY TONIGHT AND WEDNESDAY FOR
ZNS...4...6...11