NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260810_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 08/10 18Z 0.59 1907  79  66  14 0.00
Mon 08/10 19Z 1.22 2008  76  70  15 0.00
Mon 08/10 20Z 1.04 2111  72  72  15 0.00
Mon 08/10 21Z 0.50 2111  66  80  16 0.00
Mon 08/10 22Z 0.37 2112  61  78  16 0.00
Mon 08/10 23Z 0.45 2114  66  63  16 0.00
Tue 08/11 00Z 0.59 2117  72  62  16 0.00
Tue 08/11 01Z 0.82 2221  82  64  15 0.00
Tue 08/11 02Z 0.84 2324  92  65  15 0.00
Tue 08/11 03Z 0.90 2524  91  66  15 0.01
Tue 08/11 04Z 0.80 2624  89  53  15 0.01
Tue 08/11 05Z 0.70 2823  86  50  15 0.01
Tue 08/11 06Z 0.69 2823  85  51  15 0.01
Tue 08/11 07Z 0.67 2823  85  50  14 0.01
Tue 08/11 08Z 0.68 2924  88  50  14 0.01
Tue 08/11 09Z 0.64 2922  90  48  13 0.01
Tue 08/11 10Z 0.62 2922  91  41  13 0.01
Tue 08/11 11Z 0.61 3022  91  40  12 0.01
Tue 08/11 12Z 0.58 3021  92  36  12 0.01
Tue 08/11 13Z 0.55 3020  92  33  11 0.01
Tue 08/11 14Z 0.55 3019  91  30  11 0.01
Tue 08/11 15Z 0.57 3017  90  29  11 0.01
Tue 08/11 16Z 0.66 3017  88  31  11 0.01
Tue 08/11 17Z 1.68 3016  88  30  11 0.00
Tue 08/11 18Z 4.11 3016  86  25  11 0.00
Tue 08/11 19Z 4.55 3015  84  23  11 0.00
Tue 08/11 20Z 5.33 3016  82  24  12 0.00
Tue 08/11 21Z 4.12 3016  81  23  12 0.00
Tue 08/11 22Z 2.74 3017  79  25  12 0.00
Tue 08/11 23Z 1.99 3018  77  23  11 0.00
Wed 08/12 00Z 1.56 3019  77  20  11 0.00
Wed 08/12 01Z 1.25 3021  78  22  11 0.00
Wed 08/12 02Z 1.11 3122  76  21  11 0.00
Wed 08/12 03Z 0.90 3221  77  20  11 0.00
Wed 08/12 04Z 0.73 3220  74  25  11 0.00
Wed 08/12 05Z 0.71 3119  76  29  11 0.00
Wed 08/12 06Z 0.71 3118  78  25  10 0.00
Wed 08/12 07Z 0.64 3117  79  24  10 0.00
Wed 08/12 08Z 0.59 3117  79  21  10 0.00
Wed 08/12 09Z 0.53 3117  79  20  10 0.00
Wed 08/12 10Z 0.49 3117  78  21  10 0.00
Wed 08/12 11Z 0.47 3116  78  22  10 0.00
Wed 08/12 12Z 0.42 3115  79  22  10 0.00
Wed 08/12 13Z 0.36 3212  79  23  10 0.00
Wed 08/12 14Z 0.56 3109  80  24  10 0.00
Wed 08/12 15Z 1.53 3007  79  25  10 0.00
Wed 08/12 16Z 3.06 2908  79  29  10 0.00
Wed 08/12 17Z 3.44 2907  76  35  11 0.00
Wed 08/12 18Z 3.21 2907  73  48  11 0.00
Wed 08/12 19Z 2.90 2807  74  55  11 0.00
Wed 08/12 20Z 2.00 2807  78  51  11 0.00
Wed 08/12 21Z 1.08 2708  80  49  11 0.00
Wed 08/12 22Z 0.61 2708  82  47  11 0.00
Wed 08/12 23Z 0.54 2709  81  52  11 0.00
Thu 08/13 00Z 0.56 2710  82  57  11 0.00
Thu 08/13 01Z 0.53 2710  83  62  11 0.00
Thu 08/13 02Z 0.51 2709  85  74  11 0.00
Thu 08/13 03Z 0.52 2810  88  80  11 0.04
Thu 08/13 04Z 0.42 2909  92  86  11 0.08
Thu 08/13 05Z 0.33 3109  90  86  11 0.27

Run total areal avg QPF for the greens is: 0.53 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