National Weather Service United States Department of Commerce

Extreme Heat Continues; Severe Thunderstorms into Upper Midwest; Strong Bering Sea Storm

Wildfires and poor air quality continue for the Pacific Northwest, Rockies and extended into the Plains. Severe thunderstorms possible for the northern Plains and upper Midwest on Monday along a frontal boundary. Another boundary will focus showers and thunderstorms for the eastern seaboard with localized heavy rainfall possible. For Alaska, a strong Bering Sea storm will bring winds and rainfall. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260802_1200
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)
=== ===== === ==== ==== === === === ====
Sun 08/02 12Z 0.28 2013  83  65  15 0.00
Sun 08/02 13Z 0.30 2014  82  59  15 0.00
Sun 08/02 14Z 0.33 1913  86  54  15 0.00
Sun 08/02 15Z 0.56 1913  92  62  15 0.00
Sun 08/02 16Z 0.31 1814  94  72  15 0.01
Sun 08/02 17Z 0.52 1917  94  79  15 0.03
Sun 08/02 18Z 0.60 1918  93  77  15 0.04
Sun 08/02 19Z 0.68 1819  89  44  15 0.00
Sun 08/02 20Z 0.75 1820  86  23  15 0.00
Sun 08/02 21Z 0.50 1822  87  16  15 0.01
Sun 08/02 22Z 0.29 1823  83  14  16 0.00
Sun 08/02 23Z 0.23 1824  82   9  16 0.00
Mon 08/03 00Z 0.21 1824  81  13  16 0.00
Mon 08/03 01Z 0.22 1824  80  52  16 0.00
Mon 08/03 02Z 0.27 1924  76  79  16 0.00
Mon 08/03 03Z 0.30 1924  75  92  15 0.00
Mon 08/03 04Z 0.25 1922  78  92  16 0.00
Mon 08/03 05Z 0.31 1924  81  91  16 0.00
Mon 08/03 06Z 0.44 1926  90  92  15 0.02
Mon 08/03 07Z 0.32 1925  88  79  15 0.08
Mon 08/03 08Z 0.33 1925  81  82  16 0.01
Mon 08/03 09Z 0.20 1825  84  90  16 0.01
Mon 08/03 10Z 0.24 1828  93  96  16 0.03
Mon 08/03 11Z 0.30 1831  98  94  16 0.10
Mon 08/03 12Z 0.51 2031  96  83  16 0.13
Mon 08/03 13Z 0.66 2030  94  73  16 0.05
Mon 08/03 14Z 0.64 2028  98  74  16 0.02
Mon 08/03 15Z 0.78 2225  99  78  16 0.03
Mon 08/03 16Z 0.74 2223  99  78  16 0.04
Mon 08/03 17Z 0.80 2222  97  78  16 0.11
Mon 08/03 18Z 0.65 2317  95  86  16 0.16
Mon 08/03 19Z 0.57 2417  92  81  15 0.28
Mon 08/03 20Z 0.63 2319  94  69  15 0.02
Mon 08/03 21Z 0.93 2524  97  72  14 0.08
Mon 08/03 22Z 0.92 2827  97  67  12 0.08
Mon 08/03 23Z 0.69 3027  94  36  11 0.01
Tue 08/04 00Z 0.45 3129  92  25  12 0.01
Tue 08/04 01Z 0.33 3228  92  19  11 0.01
Tue 08/04 02Z 0.27 3226  88  18  11 0.00
Tue 08/04 03Z 0.31 3224  82   9  11 0.00
Tue 08/04 04Z 0.38 3124  81   4  11 0.00
Tue 08/04 05Z 0.44 3122  82   2  11 0.00
Tue 08/04 06Z 0.46 3022  82   3  11 0.00
Tue 08/04 07Z 0.47 3022  79   2  11 0.00
Tue 08/04 08Z 0.45 3022  76   2  11 0.00
Tue 08/04 09Z 0.41 3021  71   1  12 0.00
Tue 08/04 10Z 0.36 3020  64   2  13 0.00
Tue 08/04 11Z 0.33 3018  58   2  13 0.00
Tue 08/04 12Z 0.31 3018  56   2  13 0.00
Tue 08/04 13Z 0.29 3016  55   1  13 0.00
Tue 08/04 14Z 0.25 3115  52   1  13 0.00
Tue 08/04 15Z 0.23 3112  51   1  13 0.00
Tue 08/04 16Z 0.20 3109  47   1  14 0.00
Tue 08/04 17Z 0.20 3008  44   1  14 0.00
Tue 08/04 18Z 0.16 3006  42   2  15 0.00
Tue 08/04 19Z 0.15 2905  41   3  15 0.00
Tue 08/04 20Z 0.17 2804  39   5  16 0.00
Tue 08/04 21Z 0.15 2603  37   7  16 0.00
Tue 08/04 22Z 0.12 2503  35  10  17 0.00
Tue 08/04 23Z 0.13 2404  35  13  17 0.00

Run total areal avg QPF for the Central_Greens is: 1.37 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