NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260718_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)
=== ===== === ==== ==== === === === ====
Sat 07/18 18Z 0.48 2027  91  94  14 0.00
Sat 07/18 19Z 0.59 2127  97  91  14 0.01
Sat 07/18 20Z 0.62 2126  99  91  15 0.04
Sat 07/18 21Z 0.71 2226  99  91  15 0.06
Sat 07/18 22Z 0.76 2326  98  86  15 0.10
Sat 07/18 23Z 0.80 2427  97  84  16 0.05
Sun 07/19 00Z 0.80 2328  97  71  16 0.03
Sun 07/19 01Z 0.91 2428  97  85  16 0.05
Sun 07/19 02Z 0.98 2429  96  77  15 0.18
Sun 07/19 03Z 1.03 2430  96  58  15 0.04
Sun 07/19 04Z 0.95 2629  97  44  15 0.03
Sun 07/19 05Z 0.87 2829  98  58  14 0.04
Sun 07/19 06Z 0.71 3028  98  75  12 0.06
Sun 07/19 07Z 0.49 3127  95  44  10 0.03
Sun 07/19 08Z 0.38 3228  90  12   9 0.01
Sun 07/19 09Z 0.33 3230  89   9   8 0.01
Sun 07/19 10Z 0.31 3231  92   9   8 0.01
Sun 07/19 11Z 0.30 3231  91   8   8 0.01
Sun 07/19 12Z 0.31 3229  90   7   8 0.01
Sun 07/19 13Z 0.31 3227  91   5   8 0.01
Sun 07/19 14Z 0.32 3224  91   3   7 0.01
Sun 07/19 15Z 0.31 3221  88   1   7 0.00
Sun 07/19 16Z 0.47 3219  85   4   7 0.00
Sun 07/19 17Z 5.19 3117  80   7   7 0.00
Sun 07/19 18Z 6.71 3017  72  10   7 0.00
Sun 07/19 19Z 7.36 3016  69  13   8 0.00
Sun 07/19 20Z 9.22 3018  67  12   8 0.00
Sun 07/19 21Z 9.84 3019  66   6   8 0.00
Sun 07/19 22Z 8.92 3019  67   6   9 0.00
Sun 07/19 23Z 3.70 3021  66   5   9 0.00
Mon 07/20 00Z 1.63 3122  62   4   8 0.00
Mon 07/20 01Z 1.50 3124  63   4   8 0.00
Mon 07/20 02Z 1.37 3125  69   4   8 0.00
Mon 07/20 03Z 1.14 3126  73   6   7 0.00
Mon 07/20 04Z 0.79 3125  71   7   7 0.00
Mon 07/20 05Z 0.65 3123  73   7   7 0.00
Mon 07/20 06Z 0.53 3221  76   8   7 0.00
Mon 07/20 07Z 0.40 3220  75   8   8 0.00
Mon 07/20 08Z 0.38 3219  75  11   8 0.00
Mon 07/20 09Z 0.39 3117  73  14   8 0.00
Mon 07/20 10Z 0.36 3115  72  15   8 0.00
Mon 07/20 11Z 0.35 3014  71  17   8 0.00
Mon 07/20 12Z 0.39 3013  72  20   8 0.00
Mon 07/20 13Z 0.45 2913  75  23   8 0.00
Mon 07/20 14Z 0.52 2811  74  25   8 0.00
Mon 07/20 15Z 1.03 2709  74  26   8 0.00
Mon 07/20 16Z 2.22 2608  73  25   8 0.00
Mon 07/20 17Z 2.71 2507  72  23   9 0.00
Mon 07/20 18Z 2.66 2407  72  21  10 0.00
Mon 07/20 19Z 2.63 2307  71  22  10 0.00
Mon 07/20 20Z 2.09 2308  71  24  11 0.00
Mon 07/20 21Z 1.25 2108  69  25  11 0.00
Mon 07/20 22Z 0.63 2110  66  21  11 0.00
Mon 07/20 23Z 0.48 2111  61  17  11 0.00
Tue 07/21 00Z 0.42 2013  55  12  12 0.00
Tue 07/21 01Z 0.42 2015  54  12  12 0.00
Tue 07/21 02Z 0.54 2117  58  15  12 0.00
Tue 07/21 03Z 0.58 2119  56  18  12 0.00
Tue 07/21 04Z 0.65 2121  58  18  12 0.00
Tue 07/21 05Z 0.73 2222  69  20  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.79 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