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_1800
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 18Z 0.30 1913  92  65  15 0.00
Sun 08/02 19Z 0.47 1914  91  57  15 0.04
Sun 08/02 20Z 0.49 1916  89  38  15 0.04
Sun 08/02 21Z 0.42 1819  88  35  15 0.01
Sun 08/02 22Z 0.33 1820  91  49  15 0.01
Sun 08/02 23Z 0.41 1921  89  49  15 0.01
Mon 08/03 00Z 0.31 1823  86  59  15 0.00
Mon 08/03 01Z 0.29 1824  84  72  16 0.00
Mon 08/03 02Z 0.28 1924  80  80  16 0.00
Mon 08/03 03Z 0.31 1924  84  84  15 0.01
Mon 08/03 04Z 0.31 1922  86  92  15 0.01
Mon 08/03 05Z 0.27 1921  86  90  16 0.01
Mon 08/03 06Z 0.24 1921  84  89  16 0.01
Mon 08/03 07Z 0.27 1922  88  76  16 0.01
Mon 08/03 08Z 0.28 1923  91  91  16 0.01
Mon 08/03 09Z 0.25 1922  90  84  17 0.01
Mon 08/03 10Z 0.20 1823  94  90  16 0.02
Mon 08/03 11Z 0.20 1825  95  85  16 0.09
Mon 08/03 12Z 0.35 1925  92  88  16 0.03
Mon 08/03 13Z 0.33 1923  94  86  16 0.01
Mon 08/03 14Z 0.38 1922  97  79  16 0.01
Mon 08/03 15Z 0.43 2022  98  82  16 0.01
Mon 08/03 16Z 0.56 2123  98  81  16 0.02
Mon 08/03 17Z 0.71 2123  98  74  16 0.02
Mon 08/03 18Z 0.77 2123  98  72  16 0.02
Mon 08/03 19Z 0.72 2122  96  80  16 0.08
Mon 08/03 20Z 0.70 2227  88  50  16 0.30
Mon 08/03 21Z 1.14 2329  97  52  14 0.02
Mon 08/03 22Z 1.20 2530  96  70  13 0.03
Mon 08/03 23Z 1.18 2731  97  76  12 0.05
Tue 08/04 00Z 0.96 2931  97  71  11 0.06
Tue 08/04 01Z 0.73 3029  97  80  11 0.04
Tue 08/04 02Z 0.58 3129  97  58  11 0.02
Tue 08/04 03Z 0.48 3128  93  30  10 0.00
Tue 08/04 04Z 0.38 3227  87  17  10 0.00
Tue 08/04 05Z 0.49 3126  83   5  10 0.00
Tue 08/04 06Z 0.62 3128  80   7  11 0.00
Tue 08/04 07Z 0.64 3129  77   4  11 0.00
Tue 08/04 08Z 0.63 3128  75   4  11 0.00
Tue 08/04 09Z 0.53 3126  70   3  12 0.00
Tue 08/04 10Z 0.49 3124  66   3  12 0.00
Tue 08/04 11Z 0.43 3022  63   3  12 0.00
Tue 08/04 12Z 0.35 3020  55   3  13 0.00
Tue 08/04 13Z 0.32 3019  51   2  14 0.00
Tue 08/04 14Z 0.31 3117  50   2  13 0.00
Tue 08/04 15Z 0.31 3015  49   2  14 0.00
Tue 08/04 16Z 0.26 3012  46   1  14 0.00
Tue 08/04 17Z 0.27 3010  47   1  14 0.00
Tue 08/04 18Z 0.23 2908  46   1  15 0.00
Tue 08/04 19Z 0.20 2906  44   1  16 0.00
Tue 08/04 20Z 0.18 2805  41   2  16 0.00
Tue 08/04 21Z 0.19 2705  40   2  16 0.00
Tue 08/04 22Z 0.19 2605  40   1  16 0.00
Tue 08/04 23Z 0.18 2405  42   1  16 0.00
Wed 08/05 00Z 0.22 2406  45   1  16 0.00
Wed 08/05 01Z 0.19 2406  43   1  16 0.00
Wed 08/05 02Z 0.18 2405  44   1  16 0.00
Wed 08/05 03Z 0.16 2305  43   1  16 0.00
Wed 08/05 04Z 0.10 2105  37   1  17 0.00
Wed 08/05 05Z 0.10 2006  33   1  17 0.00

Run total areal avg QPF for the Central_Greens is: 1.01 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