046
FGUS75 KCYS 142220
ESFCYS
NEC007-013-033-045-105-123-157-165-WYC001-007-009-015-021-027-031-
141900-
PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE CHEYENNE WY
420PM MST THU MAR 14 2024
..SPRING FLOOD AND WATER RESOURCES OUTLOOK NUMBER 3
..BELOW-AVERAGE POTENTIAL FOR ICE JAM FLOODING THIS SPRING
..BELOW-AVERAGE POTENTIAL FOR SPRING SNOW MELT RUNOFF FLOODING
THIS SPRING FLOOD AND WATER RESOURCES OUTLOOK IS THE THIRD OF THREE
ROUTINE ISSUANCES FOR THE CHEYENNE HYDROLOGIC SERVICE AREA WHICH
COMPRISES SEVEN COUNTIES IN SOUTHEAST WYOMING AND EIGHT COUNTIES IN
THE NEBRASKA PANHANDLE. THIS OUTLOOK INCLUDES THE NORTH PLATTE RIVER
MAIN STEM AND ITS TRIBUTARIES (THE LARAMIE, ENCAMPMENT, AND MEDICINE
BOW RIVERS), THE NIOBRARA, WHITE AND LITTLE SNAKE RIVERS.
FLOOD OUTLOOK SUMMARY
THERE IS A BELOW-AVERAGE POTENTIAL FOR FLOODING EARLY THIS SPRING
DUE TO LOW-ELEVATION SNOW MELT, ICE BREAK UP, AND ICE JAMS. THESE
NORMALLY OCCUR BETWEEN FEBRUARY AND APRIL. THE WINTER HAS BROUGHT
EXTENDED PERIODS OF ABOVE-NORMAL TEMPERATURES ALONG WITH LIMITED
LOW-ELEVATION SNOW PACK. THIS LIMITS THE CHANCES FOR FLOODING DUE TO
LOW-ELEVATION SNOW MELT OR ICE JAMS DURING PERIODS OF ICE BREAK-UP
ON AREA LAKES AND RIVERS.
THE POTENTIAL FOR FLOODING DUE TO SNOW MELT RUNOFF IN SOUTHEAST
WYOMING AND THE NEBRASKA PANHANDLE THIS SPRING IS NEAR-NORMAL.
AT THIS TIME, THE SNOW PACK IN THE SOUTHERN LARAMIE RANGE IS ONLY
52 TO 62 PERCENT OF THE LONG-TERM MEDIAN. THIS WILL LIMIT THE
POTENTIAL FOR SNOW MELT FLOODING IN THE SOUTH PLATTE RIVER BASIN.
IN THE LARAMIE AND NORTH PLATTE RIVER BASINS THE SNOW PACKS ARE AT
101 AND 109 PERCENT OF THE MEDIAN. IN THE LITTLE SNAKE BASIN THE
SNOW PACK IS AT 115 PERCENT OF THE MEDIAN. THESE NUMBERS HAVE
IMPROVED OVER THE LAST FOUR WEEKS. NEAR-NORMAL SNOW PACKS IN
SOUTHEASTERN WYOMING GENERALLY TRANSLATE INTO A LOW PROBABILITY OF
FLOODING. HOWEVER, A LOW PROBABILITY OF FLOODING IS RELATIVELY
NORMAL FOR THIS REGION. THERE REMAINS CONSIDERABLE OPPORTUNITY FOR
FURTHER ACCUMULATION OF SNOW PACK BEFORE THE EXPECTED HIGH-ELEVATION
SNOW MELT IN MAY AND JUNE.
A NORMAL OR EVEN LOW PROBABILITY OF FLOODING DOES NOT MEAN THERE IS
NO CHANCE OF FLOODING. EVEN A LIGHTER SNOW PACK CAN GENERATE FLOODING
IF THERE IS A PERIOD OF EXTREMELY WARM TEMPERATURES AND/OR
SIGNIFICANT RAINFALL BEFORE THE GROUND THAWS. ONCE THE GROUND HAS
THAWED, THE FLOOD POTENTIAL FOR THE REST OF THE SPRING AND EARLY
SUMMER WILL REMAIN BELOW NORMAL.
WHILE THE SNOW PACK IS CURRENTLY NEAR NORMAL. THE POTENTIAL FOR
FLOODING, EARLY OR LATE IN THE SEASON, WILL DEPEND ON FUTURE
SNOWFALL, TEMPERATURE PATTERNS, AND SPRING RAINFALL. ALL OF THESE
FACTORS AFFECT THE TOTAL AMOUNT OF WATER STORED IN THE SNOW PACK AND
THE SPEED WITH WHICH IT IS RELEASED TO THE RIVERS.
OBSERVED AND FORECAST TEMPERATURES AND PRECIPITATION
WEATHER PATTERNS SINCE NOVEMBER HAVE BEEN EXTREMELY WARM. IN THE
LAST 60 DAYS THEY HAVE ALSO BEEN EXTREMELY WET. THIS SETS OFF A
PREDOMINANTLY DRY PERIOD EARLIER THIS WINTER.
SNOW COVER AND LIQUID WATER CONTENT
MOUNTAIN SNOW PACK ACROSS SOUTHEAST WYOMING IS BELOW NORMAL TO
NORMAL ACROSS MOST OF SOUTHEAST WYOMING. IN SOUTHEASTERN WYOMING
BASIN SNOW WATER EQUIVALENTS, MEASURED AT THE NATURAL RESOURCE
CONSERVATION SERVICE (NRCS) SNOTEL STATIONS, RANGED FROM 52
PERCENT OF MEDIAN IN THE SOUTH PLATTE RIVER BASIN IN SOUTHEAST
WYOMING TO 115 PERCENT OF MEDIAN IN THE LITTLE SNAKE RIVER BASIN.
THERE REMAINS ALMOST A MONTH UNTIL THE MEDIAN DATE OF PEAK SNOW
PACK IN MOST BASINS ACROSS THE AREA. MARCH AND APRIL CAN
HAVE A DISPROPORTIONATE AFFECT ON THE FINAL SNOW PACK ACCUMULATION
FOR THE SEASON SO WATER SUPPLY FORECASTS CAN STILL CHANGE. WARM,
WINDY TEMPERATURES OR LATE WINTER AND EARLY SPRING STORMS CAN CAUSE
DRAMATIC, LATE-SEASON, CHANGES IN TOTAL SNOW PACK.
SNOW COVER ACROSS THE NEBRASKA PANHANDLE COUNTIES IS EXTREMELY LIGHT
AND INCONSISTENT. SNOW PACK THERE CONTAINS RELATIVELY SMALL AMOUNTS
OF WATER AND SHOULD NOT BE A MAJOR FACTOR IN SPRING FLOODING.
SOIL CONDITIONS AND DROUGHT
SOIL MOISTURE IN THE AREA, AS PORTRAYED BY THE CPC, VARIES FROM NEAR
MEDIAN TO ABOVE MEDIAN WITH A SMALL EXCEPTION OF BELOW MEDIAN SOIL
MOISTURE IN SOUTH-CENTRAL WYOMING. NORMAL OR ABOVE-NORMAL CONDITIONS
ARE PREVALENT ACROSS SOUTHEASTERN WY AND THE NEBRASKA PANHANDLE.
MODERATE SEVERE DROUGHT CONDITIONS CONTINUE TO LINGER IN CARBON AND
ALBANY COUNTIES BUT HAVE IMPROVED CONSIDERABLY IN THE LAST MONTH.
DRY CONDITIONS HAVE EXPANDED SOUTHWARD INTO CONVERSE AND NIOBRARA
COUNTIES BUT REMAIN ONLY ABNORMALLY DRY AND HAVE NOT YET DEVELOPED
INTO DROUGHT. NO AREAS IN NEBRASKA ARE SHOWN TO BE AFFECTED BY
ABNORMALLY DRY OR DROUGHT CONDITIONS.
LAKE AND RIVER CONDITIONS
IT HAS BEEN AN EXCEPTIONALLY WARM WINTER WITH ONLY SHORT PERIODS OF
EXTREMELY COLD WEATHER. DESPITE THIS, MOST OF THE HIGHER ELEVATIONS
LAKES ARE ICED OVER, ALTHOUGH THE ICE THICKNESS MIGHT BE LESS THAN
IN MOST YEARS. LOWER ELEVATIONS RIVERS AND LAKES HAVE LESS ICE THAN
NORMAL WITH LARGE AREAS OF OPEN WATER.
CLIMATE OUTLOOKS
OUTLOOKS BY THE CLIMATE PREDICTION CENTER (CPC) FOR THE PERIOD FROM
6 TO 14 DAYS INDICATE CONDITIONS THAT FAVOR BELOW-NORMAL
TEMPERATURES AND ABOVE-NORMAL PRECIPITATION. THE LATEST ONE AND
3-MONTH OUTLOOKS FOR MARCH THROUGH MAY INDICATE A MODERATE TO
STRONG WET SIGNAL EARLY IN THE PERIOD AND THEN A RETURN TO
NEAR-EQUAL CHANCES OF ABOVE, BELOW, OR NEAR NORMAL PRECIPITATION.
THERE IS ONLY A WEAK SIGNAL FOR ABOVE-NORMAL TEMPERATURES DURING THE
3-MONTH PERIOD.
IN TABLE 1 BELOW, THE CURRENT (CS) AND HISTORICAL (HS) OR NORMAL
PROBABILITIES OF EXCEEDING MINOR...MODERATE...AND MAJOR FLOOD STAGE
ARE LISTED FOR THE VALID TIME PERIOD.
CS VALUES INDICATE THE PROBABILITY OF REACHING A FLOOD CATEGORY
BASED ON CURRENT CONDITIONS.
HS VALUES INDICATE THE PROBABILITY OF REACHING A FLOOD CATEGORY
BASED ON HISTORICAL OR NORMAL CONDITIONS.
WHEN THE VALUE OF CS IS GREATER THAN HS...THE PROBABILITY OF
EXCEEDING THAT LEVEL IS HIGHER THAN NORMAL. WHEN THE VALUE OF CS IS
LESS THAN HS...THE PROBABILITY OF EXCEEDING THAT LEVEL IS LOWER
THAN NORMAL.
..TABLE 1--PROBABILITIES FOR MINOR...MODERATE AND MAJOR FLOODING
VALID PERIOD: 03/16/2024 - 09/30/2024
: CURRENT AND HISTORICAL
: CHANCES OF EXCEEDING
: FLOOD CATEGORIES
: AS A PERCENTAGE (%)
CATEGORICAL :
FLOOD STAGES (FT) : MINOR MODERATE MAJOR
LOCATION MINOR MOD MAJOR : CS HS CS HS CS HS
-------- ----- ----- ----- : --- --- --- --- --- ---
:ENCAMPMENT RIVER
ENCAMPMENT 6.5 7.5 8.5 : <5 <5 <5 <5 <5 <5
:NORTH PLATTE RIVER
SARATOGA 8.5 9.5 10.5 : 33 40 11 17 <5 <5
SINCLAIR 9.0 10.0 11.0 : 27 31 11 17 5 6
:MEDICINE BOX RIVER
HANNA 6.0 7.0 8.0 : <5 <5 <5 <5 <5 <5
:NORTH PLATTE RIVER
GLENROCK 7.0 8.0 9.0 : <5 <5 <5 <5 <5 <5
ORIN 8.0 9.0 10.0 : <5 <5 <5 <5 <5 <5
:LARAMIE RIVER
WOODS LANDING 6.0 6.5 7.0 : <5 5 <5 <5 <5 <5
LARAMIE 9.0 10.0 11.0 : 13 21 <5 6 <5 <5
BOSLER 7.5 8.5 9.5 : <5 8 <5 <5 <5 <5
FORT LARAMIE 7.0 8.0 9.0 : <5 7 <5 <5 <5 <5
:NORTH PLATTE RIVER
HENRY 5.5 6.5 7.5 : <5 <5 <5 <5 <5 <5
MITCHELL 7.5 8.5 9.5 : 6 14 <5 9 <5 5
MINATARE 7.5 8.5 9.5 : <5 6 <5 <5 <5 <5
BRIDGEPORT 9.5 10.0 10.5 : <5 <5 <5 <5 <5 <5
LEGEND
CS = CONDITIONAL SIMULATION (CURRENT OUTLOOK)
HS = HISTORICAL SIMULATION
FT = FEET
IN TABLE 2 BELOW...THE 95 THROUGH 5 PERCENT COLUMNS INDICATE THE
PROBABILITY OF EXCEEDING THE LISTED STAGE LEVELS (FT) FOR THE VALID
TIME PERIOD.
..TABLE 2--EXCEEDANCE PROBABILITIES
CHANCE OF EXCEEDING STAGES
AT SPECIFIC LOCATIONS
VALID PERIOD: 03/16/2024 - 09/30/2024
LOCATION 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:ENCAMPMENT RIVER
ENCAMPMENT 4.2 4.6 4.8 4.9 5.3 5.5 6.1
:NORTH PLATTE RIVER
SARATOGA 6.3 6.7 7.5 8.2 8.9 9.6 10.2
SINCLAIR 5.6 6.0 7.0 8.0 9.1 10.2 11.2
:MEDICINE BOX RIVER
HANNA 3.2 3.2 3.7 4.2 4.4 5.0 5.2
:NORTH PLATTE RIVER
GLENROCK 2.9 2.9 3.0 3.1 3.3 3.5 4.5
ORIN 4.9 4.9 5.0 5.1 5.2 5.6 5.9
:LARAMIE RIVER
WOODS LANDING 2.0 2.2 2.6 3.2 3.5 4.2 4.8
LARAMIE 4.7 5.1 6.8 7.9 8.3 9.2 9.5
BOSLER 1.3 1.6 2.3 4.4 5.7 6.5 6.9
FORT LARAMIE 3.0 3.2 3.4 3.5 4.3 5.7 6.4
:NORTH PLATTE RIVER
HENRY 3.6 3.6 3.7 3.8 4.0 4.1 4.5
MITCHELL 2.8 2.9 3.0 3.5 4.3 5.9 7.7
MINATARE 3.5 3.6 3.9 4.4 4.8 5.6 6.8
BRIDGEPORT 4.9 5.0 5.2 5.5 5.9 6.4 7.2
IN TABLE 3 BELOW...THE 95 THROUGH 5 PERCENT COLUMNS INDICATE THE
PROBABILITY OF FALLING BELOW THE LISTED STAGE LEVELS (FT) FOR
THE VALID TIME PERIOD.
..TABLE 3--NONEXCEEDANCE PROBABILITIES
CHANCE OF FALLING BELOW STAGES
AT SPECIFIC LOCATIONS
VALID PERIOD: 03/16/2024 - 09/30/2024
LOCATION 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:ENCAMPMENT RIVER
ENCAMPMENT 1.7 1.7 1.7 1.7 1.6 1.5 1.4
:NORTH PLATTE RIVER
SARATOGA 3.6 3.5 3.5 3.5 3.5 3.5 3.4
SINCLAIR 3.1 3.1 3.1 3.1 3.1 3.1 2.9
:MEDICINE BOX RIVER
HANNA 2.1 2.0 2.0 1.9 1.9 1.8 1.7
:NORTH PLATTE RIVER
GLENROCK 0.9 0.9 0.9 0.9 0.9 0.9 0.8
ORIN 3.5 3.5 3.5 3.5 3.5 3.5 3.5
:LARAMIE RIVER
WOODS LANDING 1.2 1.2 1.2 1.1 0.3 0.3 0.3
LARAMIE 3.5 3.5 3.5 3.4 3.4 3.3 3.3
BOSLER 1.0 0.9 0.8 0.7 0.7 0.7 0.7
FORT LARAMIE 2.3 2.3 2.3 2.3 2.3 2.3 2.3
:NORTH PLATTE RIVER
HENRY 2.1 2.1 2.0 2.0 2.0 2.0 2.0
MITCHELL 0.9 0.6 0.5 0.4 0.3 0.3 0.3
MINATARE 1.8 1.7 1.6 1.5 1.4 1.4 1.4
BRIDGEPORT 3.8 3.8 3.7 3.7 3.6 3.6 3.6
THESE LONG-RANGE PROBABILISTIC OUTLOOKS CONTAIN FORECAST VALUES THAT
ARE CALCULATED USING MULTIPLE SEASON SCENARIOS FROM 30 OR MORE YEARS
OF CLIMATOLOGICAL DATA...INCLUDING CURRENT CONDITIONS OF THE
RIVER...SOIL MOISTURE...SNOW COVER AND 30 TO 90 DAY LONG-RANGE
OUTLOOKS OF TEMPERATURE AND PRECIPITATION. BY PROVIDING A RANGE
OF PROBABILITIES...THE LEVEL OF RISK ASSOCIATED WITH LONG-RANGE
PLANNING DECISIONS CAN BE DETERMINED. THESE PROBABILISTIC
FORECASTS ARE PART OF THE NATIONAL WEATHER SERVICE'S ADVANCED
HYDROLOGIC PREDICTION SERVICE.
VISIT OUR WEB SITE WEATHER.GOV/CYS FOR MORE WEATHER AND WATER
INFORMATION.
THIS IS THE FINAL WINTER SPRING FLOOD OUTLOOK OF THE SEASON. OTHER
OUTLOOKS MAY BE ISSUED THIS SPRING AS NEEDED.
AJA
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