Flooding in Utah, May 21 to 25, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
900 PM MDT FRI MAY 20 2005

.SYNOPSIS...A WEAK AND MAINLY DRY COLD FRONT WILL CROSS NORTHERN
UTAH TONIGHT. WARM AND DRY HIGH PRESSURE ALOFT WILL CENTER OVER THE
INTERIOR WEST INTO NEXT WEEK.

&&

.DISCUSSION...SOME SHOWERS AND A FEW THUNDERSTORMS HAVE MOVED ACROSS
FAR NORTHWEST UTAH SINCE LATE AFTERNOON SIMILAR TO PAST COUPLE DAYS.
THESE STORMS HAVE BECOME STRONG TO SEVERE IN IDAHO WHERE MSAS
DEPICTS THE MOST UNSTABLE AIR MASS AND BEST SHEAR...WHICH IS
SOUTHEAST OF STRONG BAROCLINIC ZONE IN CENTRAL IDAHO. SMALL THREAT
FOR CONVECTION TO CONTINUE THIS EVENING IN THE FAR NORTH. THERE IS
INSTABILITY OVER THE WASATCH FRONT PER ANALYSIS BUT LACK OF LOW
LEVEL MOISTURE GIVES VERY HIGH LEVEL OF FREE CONVECTION AND ALL THAT
HAS DEVELOPED IS ALTOCUMULUS CASTELLANUS. A FEW RECORDS WERE BROKEN
TODAY IN UTAH (RERSLC)...AND ANOTHER DAY IN THE SL VALLEY WITH
SOUTHERLY FLOW PREVENTING THE SEA BREEZE FRONT FROM MOVING SOUTH OF
THE LAKE SHORE. WINDS OVER THE RIDGES HAVE GUST OVER 50 MPH TODAY.
OBSERVED 700 MB TEMPS OF 12C AT KSLC DRY ADIABATICALLY GAVE US 89F
FOR THE HIGH...SHY OF THE RECORD 92F. FURTHER NW IT WAS -1C AT
BOISE. SURFACE COLD FRONT LIES OVER THE WEST DESERTS AND IS STILL
PROGGED TO PUSH EAST ACROSS NORTHERN UTAH LATER THIS EVENING AS AN
UPPER LEVEL SHORT WAVE PER WATER VAPOR AND MODELS LIFTS E-NE ACROSS
IDAHO. THE FRONT GETS THE BEST PUSH AFTER MIDNIGHT AS NVA SUBSIDENCE
SPREADS OVER NORTHERN UTAH AND SURFACE PRESSURE RISES OCCUR.

BAROCLINIC ZONE WILL COOL 700 MB TEMPS TO 4C OVER THE GSL EARLY
SATURDAY UNDER A PERIOD OF NW FLOW ALOFT BUT THEY RECOVER TO 8C BY
AFTERNOON AS HEIGHTS ALOFT BUILD AGAIN AND FLOW BECOMES SW
ALOFT...THOUGH LOW LEVEL NORTHWEST WILL DOMINATE. AIR MASS OVER THE
SOUTH WHERE IT WAS 14-16C TODAY DOES NOT CHANGE SO UPPER 90S AGAIN
IN THE HOT SPOTS. GRIDS WILL NEED TO BE BUMPED UP HERE. UPPER RIDGE
BUILDING ON SUNDAY SENDS 700 MB TEMPS BACK TO 12C IN THE NORTH BY
AFTERNOON AND SURFACE NORTHERLY FLOW WEAKENS. SHORT WAVE RIDING BY
WELL TO THE NORTH IN THE WESTERLIES PUTS A DENT TO THE UPPER RIDGE
MONDAY THROUGH WEDNESDAY. THIS COULD BRING SLIGHT COOLING IN THE
NORTH MONDAY PER ECMWF AND GFS THEN MORE SIGNIFICANTLY TUESDAY AND
WEDNESDAY. HOWEVER WE REMAIN IN BETWEEN THE UPPER RIDGE TO THE SOUTH
AND STORM TRACK TO THE NORTH WHICH KEEPS THE HOTTEST TEMPS ACROSS
SOUTHERN UTAH...14-17C AT 700 MB THRU WEDNESDAY.

&&

.HYDRO...SPRING RUNOFF TAKING OFF IN RESPONSE TO THE MUCH ABOVE
NORMAL TEMPERATURES REGION-WIDE. WEAK...DRY COLD FRONT MOVING ACROSS
NORTHERN UTAH TONIGHT WILL HAVE SOME AFFECT ON TEMPERATURES SATURDAY
IN THE NORTH...BUT STILL ABOVE NORMAL. THE PATTERN OVER THE INTERIOR
WEST WILL REMAIN WARM AND DRY FOR SEVERAL DAYS TO COME AND PEAK
RUNOFF SHOULD OCCUR EARLY NEXT WEEK.

&&

.AVIATION...70 PERCENT CHANCE WIND SHIFT TO W-NW AT SLC LIKELY
DELAYED UNTIL AROUND 06Z BUT MAY GO SW AT TIMES.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...FLOOD WARNING UNTIL FURTHER NOTICE UPPER SEVIER RIVER.
     FLOOD WATCH LOWER WEBER RIVER AND RIVERS OF MORGAN COUNTY
     UNTIL FURTHER NOTICE.
     FLOOD WATCH SOUTH CENTRAL UTAH UNTIL FURTHER NOTICE.
WY...NONE.

TARDY

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
500 AM MDT FRI MAY 20 2005

UTZ001>021-WYZ021-221300-
CACHE VALLEY/UTAH PORTION-CASTLE COUNTRY-CENTRAL AND SOUTHWEST
MOUNTAINS-GLEN CANYON RECREATION AREA/LAKE POWELL-GREAT SALT LAKE
DESERT AND MOUNTAINS-HENRY MOUNTAINS-NORTHERN WASATCH FRONT-SALT LAKE
AND TOOELE VALLEYS-SAN RAFAEL SWELL-SANPETE/SEVIER VALLEYS-SOUTH
CENTRAL UTAH-SOUTHERN WASATCH FRONT-SOUTHWEST UTAH-SOUTHWEST WYOMING-
UTAHS DIXIE AND ZION NATIONAL PARK-WASATCH MOUNTAIN VALLEYS-WASATCH
MOUNTAINS I-80 NORTH-WASATCH MOUNTAINS SOUTH OF I-80-WASATCH
PLATEAU/BOOK CLIFFS-WEST CENTRAL UTAH-WESTERN UINTA BASIN-WESTERN
UINTA MOUNTAINS-
700 AM MDT SAT MAY 21 2005

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN TWO-THIRDS OF UTAH
AND EXTREME SOUTHWEST WYOMING.

.DAY ONE... TODAY

SEASONAL OR HIGHER TEMPERATURES WILL SERVE TO INCREASE SNOW MELT
TODAY ACROSS THE REGION. MANY CREEKS AND RIVERS ARE FLOWING AT HIGH
LEVELS IN UTAH...WITH SOME FLOODING OCCURRING. REFER TO THE LATEST
FLOOD PRODUCTS FOR DETAILS ON CURRENT OR EXPECTED FLOODING.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

WARM TEMPERATURES THROUGH MUCH OF NEXT WEEK WILL KEEP THE SNOWMELT
AT A FAST PACE. ADDITIONAL FLOODING PROBLEM MAY DEVELOP AS A RESULT
OF THE RAPID SNOW MELT. LOOK FOR ADDITIONAL FLOOD PRODUCTS DURING
THE WEEK FROM THE NATIONAL WEATHER SERVICE ADDRESSING THIS
SITUATION.