National Weather Service United States Department of Commerce

Extreme Heat in the Southwest; Severe Weather in the Northern Plains; Heavy Rain in the East

Extreme heat continues across the Southwest as temperatures may top 120 degrees. The heat may expand across the West and south-central U.S. into the middle of the month. Severe thunderstorms capable of severe wind gusts and large hail will be the primary hazards today across the northern Plains into the upper Midwest. Rainfall could be locally heavy across the Eastern U.S. today. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260803_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 08/03 06Z 0.20 1823  91  99  15 0.00
Mon 08/03 07Z 0.16 1825  95  97  15 0.01
Mon 08/03 08Z 0.18 1826  97  91  16 0.02
Mon 08/03 09Z 0.17 1825  98  86  16 0.12
Mon 08/03 10Z 0.31 1926  98  86  16 0.08
Mon 08/03 11Z 0.42 2026  96  73  16 0.02
Mon 08/03 12Z 0.53 2128  97  75  17 0.01
Mon 08/03 13Z 0.64 2126  99  80  16 0.09
Mon 08/03 14Z 0.66 2224  99  72  16 0.04
Mon 08/03 15Z 0.69 2221  99  65  16 0.03
Mon 08/03 16Z 0.76 2221  98  70  16 0.02
Mon 08/03 17Z 0.83 2121  95  61  16 0.01
Mon 08/03 18Z 1.02 2123  96  77  16 0.05
Mon 08/03 19Z 1.03 2330  90  59  15 0.12
Mon 08/03 20Z 1.49 2429  90  38  14 0.00
Mon 08/03 21Z 1.44 2529  93  51  12 0.00
Mon 08/03 22Z 1.24 2729  97  68  12 0.02
Mon 08/03 23Z 1.19 2830  96  78  10 0.02
Tue 08/04 00Z 0.96 2931  96  75  10 0.02
Tue 08/04 01Z 0.71 3029  97  54  10 0.03
Tue 08/04 02Z 0.49 3129  97  15  10 0.02
Tue 08/04 03Z 0.41 3231  84   3  10 0.00
Tue 08/04 04Z 0.46 3230  75  17  10 0.00
Tue 08/04 05Z 0.63 3026  87  14  10 0.00
Tue 08/04 06Z 0.66 3028  84   2  11 0.00
Tue 08/04 07Z 0.67 3027  80   3  11 0.00
Tue 08/04 08Z 0.69 3026  75   4  11 0.00
Tue 08/04 09Z 0.70 3025  71   3  11 0.00
Tue 08/04 10Z 0.61 3124  67   3  11 0.00
Tue 08/04 11Z 0.50 3022  61   2  12 0.00
Tue 08/04 12Z 0.40 3122  57   2  13 0.00
Tue 08/04 13Z 0.33 3119  55   2  13 0.00
Tue 08/04 14Z 0.31 3117  54   2  13 0.00
Tue 08/04 15Z 0.33 3114  55   2  13 0.00
Tue 08/04 16Z 0.33 3112  55   2  12 0.00
Tue 08/04 17Z 0.37 3009  56   2  13 0.00
Tue 08/04 18Z 0.57 2907  60   2  13 0.00
Tue 08/04 19Z 0.88 2706  64   1  13 0.00
Tue 08/04 20Z 0.58 2506  63   1  14 0.00
Tue 08/04 21Z 0.34 2506  58   1  14 0.00
Tue 08/04 22Z 0.28 2406  56   1  15 0.00
Tue 08/04 23Z 0.25 2407  53   1  15 0.00
Wed 08/05 00Z 0.31 2409  53   2  15 0.00
Wed 08/05 01Z 0.32 2410  56   2  16 0.00
Wed 08/05 02Z 0.36 2411  55   2  16 0.00
Wed 08/05 03Z 0.40 2413  52   2  16 0.00
Wed 08/05 04Z 0.38 2412  51   2  16 0.00
Wed 08/05 05Z 0.36 2512  48   2  16 0.00
Wed 08/05 06Z 0.36 2513  48   2  16 0.00
Wed 08/05 07Z 0.37 2613  52   2  16 0.00
Wed 08/05 08Z 0.35 2612  50   2  15 0.00
Wed 08/05 09Z 0.35 2711  57   3  15 0.00
Wed 08/05 10Z 0.33 2610  63   3  14 0.00
Wed 08/05 11Z 0.28 2609  63   2  14 0.00
Wed 08/05 12Z 0.26 2508  62   1  14 0.00
Wed 08/05 13Z 0.31 2508  68   2  14 0.00
Wed 08/05 14Z 0.32 2408  71   2  13 0.00
Wed 08/05 15Z 0.39 2407  74   2  13 0.00
Wed 08/05 16Z 0.55 2306  71   3  14 0.00
Wed 08/05 17Z 1.05 2207  68   5  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.73 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1