May 1, 2021 Spring and Summer Streamflow Forecasts
Upper Missouri Basin
The high elevation snow pack in the Upper Missouri Basin as of May 1
was near average. The snow pack in the St. Mary Basin was 99 percent.
April precipitation across the Upper Missouri Basin was below average.
Basin precipitation sumapries for the Missouri Basin include: Milk St. Mary,
60 percent; Milk Canada, 44 percent; Lower Milk, 40 percent; above Toston,
48 percent; Toston to Ft. Peck, 63 percent.
April 2021 Upper Missouri Mean Precip Oct-Apr WY2021 Upper Missouri Mean Precip
Stream flow in the Upper Missouri Basin is forecast to be
below average during the upcoming Spring and Summer.
The St. Mary River is forecast to have 92 percent of average
May-September flows. Runoff is expected to range around
93 percent of average for the Missouri Basin above Fort Peck,
Montana.
Upper Missouri May 1, 2021 Spring and Summer Streamflow Forecasts
Of the four major irrigation reservoirs in Montana; Lima
Reservoir had 96 percent average storage, Clark Canyon was
holding 102 percent of average water, Gibson Reservoir had 94
percent of average stored water, and Fresno Reservoir had
92 percent of average stored water.
Yellowstone Basin
The high elevation snow pack in the Yellowstone Basin was near average
on May 1. The snow pack in the Upper Yellowstone Basin was 88 percent
of average. The snow packs in the Wind, Bighorn, and Shoshone Basins were 104,
102, and 69 percent of average, respectively. The snow packs in the Tongue
and Powder basins were 118 and 137 percent of average, respectively.
Precipitation during April was below to near average. The upper Yellowstone
River Basin received 74 percent of average precipitation while the
Lower Yellowstone River Basin reported 56 percent of average. The
Bighorn Basin received 103 percent of average precipitation while the
Wind River Basin received 95 percent of average. The Little Bighorn -
Upper Tongue Basin received 117 percent of average and the Powder River
had 63 percent of average precipitation.
April 2021 Yellowstone Mean Precip Oct-Apr WY2021 Yellowstone Mean Precip
Forecast stream flow in the Yellowstone Basin is below average
for the upcoming Spring and Summer. Stream flow for the
Yellowstone River above Sidney, Montana is forecast to be about
82 percent of average. Flow in the Tongue Basin is expected to be
92 percent of average. Flows in the Powder River are expected
to be about 73 percent of average.
Monthend storage at Boysen Reservoir was 111 percent of average.
Stored water in Buffalo Bill Reservoir was 124 percent of average.
Monthend storage was 102 percent of average at Bighorn Reservoir.
Yellowstone May 1, 2021 Spring and Summer Streamflow Forecasts
Platte Basin
The high elevation snow pack in the Upper North Platte Basin was
83 percent of average on May 1. The snow pack in the North Platte
Basin below Seminoe Reservoir was 130 percent of average. The snow
pack in the South Platte Basin was 102 percent of average.
Precipitation during April in the Upper North Platte Basin was 52
percent of average. In the Lower North Platte Basin, precipitation
was 57 percent of average. The North Platte Plains below Guernsy
Reservoir had 52 percent. The South Platte Mountains had 83
percent whereas the Plains had 117 percent of average April
precipitation.
April 2021 Platte Mean Precip Oct-Apr WY2021 Platte Mean Precip
Stream flow in the Platte Basin is forecast to be below
average during the upcoming Spring and Summer. Runoff
for streams above Seminoe Reservoir are expected to be
about 75 percent of average. Streams in the South Platte
Basin above South Platte, Colorado can expect 67 percent
of average flow. For the remainder of the South Platte
basin, flows are expected near 83 percent.
Stored water in the South Platte Basin was 101 percent of average
on May 1.
North Platte Streamflow Fcst South Platte Streamflow Fcst
WATER SUPPLY FORECAST
NWS MISSOURI BASIN RIVER FORECAST CENTER
PLEASANT HILL MISSOURI
0811 AM CDT WEDNESDAY MAY 05, 2021
MISSOURI/YELLOWSTONE/PLATTE RIVER BASIN FORECASTS
50% % 10% 90% AVG
FORECAST POINT PERIOD (KAF) AVG (KAF) (KAF) (KAF)
--------------------------------------------------------------------
Boysen Resvr Inflow May-Sep 577 54 943 411 1079
SBDW4N
Bighorn R at Kane May-Sep 1098 69 1609 791 1587
LVEW4N
Greybull R at Meeteetse May-Sep 113 66 175 64 170
MEEW4N
Buffalo Bill Resvr Inflow May-Sep 540 73 731 437 738
CDYW4N
St. Mary R nr Babb May-Sep 374 93 437 310 403
SMYM8N
St. Mary R at Intl Boundary May-Sep 429 85 520 351 506
SMBM8N
Milk R nr Western Crossing May-Sep 17 69 48 8 24
PDBM8N
Milk R nr Eastern Crossing May-Sep 35 75 117 17 47
ERNM8N
North Platte R nr Northgate May-Sep 144 70 229 88 207
NGTC2
Encampment R nr Encampment May-Sep 83 60 105 62 139
ECRW4
Encampment R nr Encampment May-Sep 90 61 112 69 146
ECRW4N
Rock Cr nr Arlington May-Sep 52 103 60 45 51
KCRW4
Rock Cr nr Arlington May-Sep 53 103 60 45 51
KCRW4N
Seminoe Resvr Inflow May-Sep 491 68 697 330 725
SETW4
Seminoe Resvr Inflow May-Sep 635 73 839 481 868
SETW4N
Laramie R nr Woods Landing May-Sep 53 52 93 33 101
WODW4
Laramie R nr Woods Landing May-Sep 86 65 126 65 133
WODW4N
Little Laramie R nr Filmore May-Sep 57 136 71 46 42
SMTW4
Little Laramie R nr Filmore May-Sep 59 110 73 49 54
SMTW4N
Antero Resvr Inflow May-Sep 10 63 13 7 16
ANRC2N
Spinney Mountain Resvr Inflow May-Sep 30 57 44 23 53
SPYC2N
Elevenmile Canyon Resvr Inflow May-Sep 34 61 50 25 56
EVNC2N
Cheesman Lk Inflow May-Sep 73 70 100 56 104
CHEC2N
S Platte R at S Platte May-Sep 161 85 215 132 189
SPTC2N
Bear Cr at Morrison May-Sep 23 127 33 18 18
MRRC2N
Clear Cr at Golden May-Sep 52 47 75 45 112
GLDC2N
St. Vrain Cr at Lyons May-Sep 89 98 114 78 91
LNSC2N
Boulder Cr nr Orodell May-Sep 42 86 57 39 49
OROC2N
S Boulder Cr nr Eldorado Sprgs May-Sep 27 71 43 22 38
BELC2N
Cache La Poudre at Canyon Mouth May-Sep 148 73 234 115 201
FTDC2N
Lima Resvr Inflow May-Sep 28 44 45 21 63
LRRM8N
Clark Canyon Resvr Inflow May-Sep 53 40 81 41 132
CLKM8N
Beaverhead R at Barretts May-Sep 74 46 106 62 161
BARM8N
Ruby R Resvr Inflow May-Sep 54 63 70 43 87
ALRM8N
Big Hole R nr Melrose May-Sep 436 90 653 346 482
MLRM8
Big Hole R nr Melrose May-Sep 500 101 717 410 494
MLRM8N
Hebgen Resvr Inflow May-Sep 388 105 450 341 369
HBDM8N
Ennis Resvr Inflow May-Sep 692 106 799 585 653
ELMM8N
Gallatin R nr Gateway May-Sep 354 83 457 288 424
GLGM8
Gallatin R nr Gateway May-Sep 353 83 456 287 424
GLGM8N
Gallatin R at Logan May-Sep 304 68 465 228 447
LOGM8
Gallatin R at Logan May-Sep 452 84 584 375 540
LOGM8N
Missouri R at Toston May-Sep 2017 91 2555 1701 2220
TOSM8N
Missouri R at Fort Benton May-Sep 3037 94 3766 2635 3240
FBNM8N
Missouri R nr Virgelle May-Sep 3452 93 4440 3013 3725
VRGM8N
Missouri R nr Landusky May-Sep 3697 95 4822 3214 3900
LDKM8N
Missouri R below Fort Peck Dam May-Sep 4032 98 5346 3501 4120
FPKM8N
Gibson Resvr Inflow May-Sep 454 130 625 404 349
AGSM8N
Marias R nr Shelby May-Sep 341 94 506 272 362
SHLM8N
Musselshell R at Harlowton May-Sep 51 56 88 28 92
HLWM8N
Yellowstone R at Yellowstone Lk May-Sep 422 55 503 344 767
YLOW4
Yellowstone R at Yellowstone Lk May-Sep 563 78 666 445 722
YLOW4N
Yellowstone R at Corwin Sprgs May-Sep 1193 67 1442 1010 1772
CORM8
Yellowstone R at Corwin Sprgs May-Sep 1397 81 1672 1165 1722
CORM8N
Yellowstone R at Livingston May-Sep 1454 73 1764 1242 1994
LIVM8
Yellowstone R at Livingston May-Sep 1718 85 2055 1459 2024
LIVM8N
Yellowstone R at Billings May-Sep 2273 102 2990 1931 2220
BILM8
Yellowstone R at Billings May-Sep 3175 83 3909 2788 3840
BILM8N
Yellowstone R at Miles City May-Sep 5268 79 6698 4440 6670
MILM8N
Yellowstone R at Sidney May-Sep 5420 78 6999 4588 6940
SIDM8N
Boulder R at Big Timber May-Sep 168 58 212 135 288
BTMM8
Boulder R at Big Timber May-Sep 209 69 254 179 303
BTMM8N
Stillwater R nr Absarokee May-Sep 323 68 411 263 472
SRAM8
Stillwater R nr Absarokee May-Sep 381 74 468 324 517
SRAM8N
Clks Fk Yellowstone R nr Belfry May-Sep 428 82 548 361 524
BFYM8
Clks Fk Yellowstone R nr Belfry May-Sep 499 87 620 434 572
BFYM8N
Bighorn R nr St. Xavier May-Sep 1727 64 2410 1316 2717
STXM8N
Little Bighorn R nr Hardin May-Sep 59 67 90 46 89
HRDM8N
Tongue R nr Dayton May-Sep 76 102 109 61 75
DAYW4N
Tongue R nr Decker May-Sep 169 87 254 130 193
DSLM8N
Tongue R Resvr Inflow May-Sep 169 87 257 131 195
DKRM8N
Powder R at Moorhead May-Sep 142 75 237 102 190
MHDM8N
Powder R nr Locate May-Sep 148 70 246 106 211
LOCM8N
Locations with an `N` suffix indicate natural flows excluding
stream augmentations.
KAF: Thousands of Acre-feet
%AVG: Current 50%/AVG
AVG: Average(50%) seasonal runoff voulme as simulated by the river
forecast model considering acontinuous simulation of the basin
response to historic climate data (observed precipitation and
temperatures) over the period of 1981-2010.
The 50%, 10% and 90% columns indicate the probability that the
actual volume will exceed the forecast for the valid time perion
for more information, please visit: www.weather.gov/mbrfc/water
