NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260930_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)
=== ===== === ==== ==== === === === ====
Wed 09/30 18Z 0.11 2504  98  28  11 0.00
Wed 09/30 19Z 0.13 2705  98  24  11 0.01
Wed 09/30 20Z 0.13 2705  98  26  11 0.01
Wed 09/30 21Z 0.15 2706  97  40  11 0.00
Wed 09/30 22Z 0.15 2706  94  48  11 0.00
Wed 09/30 23Z 0.17 2607  89  42  12 0.00
Thu 10/01 00Z 0.22 2609  86  42  12 0.00
Thu 10/01 01Z 0.30 2612  85  38  12 0.00
Thu 10/01 02Z 0.37 2614  89  28  11 0.00
Thu 10/01 03Z 0.41 2614  90  29  11 0.00
Thu 10/01 04Z 0.46 2715  92  34  11 0.01
Thu 10/01 05Z 0.45 2715  92  35  11 0.00
Thu 10/01 06Z 0.47 2715  94  36  11 0.00
Thu 10/01 07Z 0.48 2614  93  38  11 0.00
Thu 10/01 08Z 0.46 2514  93  40  11 0.01
Thu 10/01 09Z 0.44 2414  91  39  12 0.00
Thu 10/01 10Z 0.50 2417  93  54  12 0.00
Thu 10/01 11Z 0.48 2417  94  73  12 0.01
Thu 10/01 12Z 0.50 2318  94  83  12 0.01
Thu 10/01 13Z 0.52 2319  93  86  12 0.01
Thu 10/01 14Z 0.54 2321  92  86  12 0.01
Thu 10/01 15Z 0.65 2324  96  93  12 0.01
Thu 10/01 16Z 0.69 2324  94  94  12 0.02
Thu 10/01 17Z 0.65 2324  94  88  12 0.02
Thu 10/01 18Z 0.66 2423  89  79  13 0.01
Thu 10/01 19Z 0.73 2423  90  82  13 0.00
Thu 10/01 20Z 0.81 2425  91  95  13 0.00
Thu 10/01 21Z 0.76 2426  91  96  14 0.01
Thu 10/01 22Z 0.86 2429  90  92  14 0.02
Thu 10/01 23Z 0.89 2429  92  91  14 0.01
Fri 10/02 00Z 0.82 2428  89  88  14 0.01
Fri 10/02 01Z 0.86 2330  91  76  14 0.01
Fri 10/02 02Z 0.87 2333  91  62  15 0.01
Fri 10/02 03Z 0.97 2336  93  73  15 0.02
Fri 10/02 04Z 1.02 2437  92  85  15 0.03
Fri 10/02 05Z 1.04 2436  93  82  15 0.02
Fri 10/02 06Z 0.98 2436  91  84  15 0.03
Fri 10/02 07Z 0.95 2435  93  90  15 0.03
Fri 10/02 08Z 1.02 2436  94  90  15 0.07
Fri 10/02 09Z 1.04 2436  95  90  15 0.06
Fri 10/02 10Z 0.96 2533  96  90  14 0.07
Fri 10/02 11Z 0.85 2627  97  93  13 0.12
Fri 10/02 12Z 0.81 2625  97  95  13 0.11
Fri 10/02 13Z 0.70 2722  97  93  12 0.14
Fri 10/02 14Z 0.63 2820  98  88  12 0.09
Fri 10/02 15Z 0.51 2816  98  86  12 0.07
Fri 10/02 16Z 0.46 2815  97  80  11 0.02
Fri 10/02 17Z 0.42 2914  98  84  10 0.01
Fri 10/02 18Z 0.37 2913  95  73  10 0.02
Fri 10/02 19Z 0.35 3013  93  77  10 0.01
Fri 10/02 20Z 0.35 3014  86  60  10 0.02
Fri 10/02 21Z 0.39 3016  82  40   9 0.01
Fri 10/02 22Z 0.39 3017  79  34   8 0.00
Fri 10/02 23Z 0.44 3120  75  19   8 0.00
Sat 10/03 00Z 0.43 3122  72   6   7 0.00
Sat 10/03 01Z 0.47 3223  75   3   6 0.00
Sat 10/03 02Z 0.48 3222  87   3   6 0.00
Sat 10/03 03Z 0.52 3223  88   6   5 0.01
Sat 10/03 04Z 0.55 3224  89   7   4 0.01
Sat 10/03 05Z 0.46 3323  87   2   4 0.00

Run total areal avg QPF for the greens is: 1.18 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