Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20251123_1800
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 11/23 18Z 0.13 2209  99  82  -6 0.00
Sun 11/23 19Z 0.17 2209  98  90  -6 0.00
Sun 11/23 20Z 0.16 2308  98  90  -5 0.01
Sun 11/23 21Z 0.15 2308  98  90  -5 0.01
Sun 11/23 22Z 0.13 2207  98  89  -5 0.01
Sun 11/23 23Z 0.10 2206  97  87  -5 0.00
Mon 11/24 00Z 0.13 2406  97  85  -5 0.00
Mon 11/24 01Z 0.16 2506  96  86  -5 0.00
Mon 11/24 02Z 0.21 2706  95  88  -5 0.00
Mon 11/24 03Z 0.27 2808  94  84  -5 0.00
Mon 11/24 04Z 0.30 2809  93  85  -5 0.00
Mon 11/24 05Z 0.33 2909  94  85  -5 0.00
Mon 11/24 06Z 0.40 2911  97  85  -5 0.01
Mon 11/24 07Z 0.53 2914  98  83  -5 0.02
Mon 11/24 08Z 0.58 2916  98  79  -5 0.02
Mon 11/24 09Z 0.62 3017  98  77  -5 0.03
Mon 11/24 10Z 0.65 3019  98  71  -6 0.03
Mon 11/24 11Z 0.66 3020  98  65  -6 0.03
Mon 11/24 12Z 0.71 3022  98  56  -6 0.03
Mon 11/24 13Z 0.80 3023  98  47  -6 0.03
Mon 11/24 14Z 0.85 3024  98  62  -7 0.03
Mon 11/24 15Z 0.80 3022  98  49  -7 0.03
Mon 11/24 16Z 0.71 3020  98  28  -7 0.02
Mon 11/24 17Z 0.65 3019  96   5  -7 0.02
Mon 11/24 18Z 0.52 2918  92   2  -6 0.01
Mon 11/24 19Z 0.51 2818  89   7  -5 0.01
Mon 11/24 20Z 0.49 2920  81  10  -4 0.01
Mon 11/24 21Z 0.40 2919  65  26  -2 0.00
Mon 11/24 22Z 0.39 2919  55  38  -1 0.00
Mon 11/24 23Z 0.40 2820  45  73   0 0.00
Tue 11/25 00Z 0.40 2820  40  78   0 0.00
Tue 11/25 01Z 0.41 2720  28  93   0 0.00
Tue 11/25 02Z 0.47 2720  22  90   0 0.00
Tue 11/25 03Z 0.50 2619  28  92   0 0.00
Tue 11/25 04Z 0.42 2421  17  89   1 0.00
Tue 11/25 05Z 0.49 2426  14  91   1 0.00
Tue 11/25 06Z 0.60 2529  14  79   1 0.00
Tue 11/25 07Z 0.68 2530  14  75   1 0.00
Tue 11/25 08Z 0.70 2629  15  80   1 0.00
Tue 11/25 09Z 0.70 2629  17  77   1 0.00
Tue 11/25 10Z 0.68 2727  19  79   1 0.00
Tue 11/25 11Z 0.65 2725  22  85   1 0.00
Tue 11/25 12Z 0.60 2723  27  92   1 0.00
Tue 11/25 13Z 0.50 2621  29  92   1 0.00
Tue 11/25 14Z 0.42 2618  33  91   1 0.00
Tue 11/25 15Z 0.32 2515  35  90   2 0.00
Tue 11/25 16Z 0.25 2513  34  81   2 0.00
Tue 11/25 17Z 0.21 2413  32  72   2 0.00
Tue 11/25 18Z 0.18 2314  34  68   2 0.00
Tue 11/25 19Z 0.14 2214  36  63   2 0.00
Tue 11/25 20Z 0.12 2213  33  56   3 0.00
Tue 11/25 21Z 0.13 2213  36  71   3 0.00
Tue 11/25 22Z 0.15 2214  39  77   3 0.00
Tue 11/25 23Z 0.13 2214  39  81   3 0.00
Wed 11/26 00Z 0.13 2214  41  80   3 0.00
Wed 11/26 01Z 0.12 2213  43  72   3 0.00
Wed 11/26 02Z 0.11 2213  45  84   4 0.00
Wed 11/26 03Z 0.08 2113  49  94   4 0.00
Wed 11/26 04Z 0.08 2114  57  97   3 0.00
Wed 11/26 05Z 0.07 2114  66  97   3 0.00

Run total areal avg QPF for the Northern_Greens is: 0.36 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