NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260101_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)
=== ===== === ==== ==== === === === ====
Thu 01/01 18Z 6.98 2817  82  59 -19 0.00
Thu 01/01 19Z 8.49 2820  81  49 -19 0.00
Thu 01/01 20Z 7.30 2821  80  48 -20 0.00
Thu 01/01 21Z 4.82 2821  75  49 -20 0.00
Thu 01/01 22Z 3.01 2823  74  48 -20 0.00
Thu 01/01 23Z 1.80 2825  69  22 -21 0.00
Fri 01/02 00Z 1.37 2827  65  10 -21 0.00
Fri 01/02 01Z 1.07 2927  60   9 -21 0.00
Fri 01/02 02Z 0.92 2928  52  14 -20 0.00
Fri 01/02 03Z 0.80 2927  51  15 -20 0.00
Fri 01/02 04Z 0.68 2925  52  27 -19 0.00
Fri 01/02 05Z 0.63 2822  57  62 -19 0.00
Fri 01/02 06Z 0.60 2719  65  67 -19 0.00
Fri 01/02 07Z 0.64 2619  77  72 -19 0.00
Fri 01/02 08Z 0.68 2521  84  74 -18 0.00
Fri 01/02 09Z 0.66 2521  88  75 -18 0.00
Fri 01/02 10Z 0.63 2521  89  74 -17 0.00
Fri 01/02 11Z 0.67 2621  91  69 -18 0.00
Fri 01/02 12Z 0.72 2621  91  67 -18 0.00
Fri 01/02 13Z 0.75 2621  91  65 -18 0.00
Fri 01/02 14Z 0.81 2620  91  55 -18 0.00
Fri 01/02 15Z 1.01 2620  89  44 -18 0.00
Fri 01/02 16Z 1.89 2719  87  33 -18 0.00
Fri 01/02 17Z 6.83 2719  86  26 -18 0.00
Fri 01/02 18Z 9.99 2719  85  23 -18 0.00
Fri 01/02 19Z 9.63 2719  82  22 -18 0.00
Fri 01/02 20Z 7.56 2719  80  17 -18 0.00
Fri 01/02 21Z 3.19 2720  77  14 -18 0.00
Fri 01/02 22Z 2.01 2722  75  17 -18 0.00
Fri 01/02 23Z 2.01 2724  76  36 -18 0.00
Sat 01/03 00Z 1.81 2725  82  58 -18 0.00
Sat 01/03 01Z 1.96 2826  86  69 -18 0.00
Sat 01/03 02Z 1.87 2826  87  66 -18 0.00
Sat 01/03 03Z 2.16 2827  86  68 -18 0.00
Sat 01/03 04Z 2.30 2827  83  76 -19 0.00
Sat 01/03 05Z 1.69 2828  81  76 -19 0.00
Sat 01/03 06Z 1.69 2829  81  79 -19 0.00
Sat 01/03 07Z 1.28 2929  83  77 -19 0.00
Sat 01/03 08Z 1.27 2828  87  74 -19 0.00
Sat 01/03 09Z 1.04 2828  89  73 -19 0.00
Sat 01/03 10Z 0.96 2828  91  69 -19 0.00
Sat 01/03 11Z 0.96 2827  91  59 -19 0.00
Sat 01/03 12Z 1.12 2827  93  48 -19 0.00
Sat 01/03 13Z 1.21 2826  92  41 -20 0.00
Sat 01/03 14Z 1.46 2825  90  35 -20 0.00
Sat 01/03 15Z 1.99 2823  89  33 -21 0.00
Sat 01/03 16Z 1.54 2821  89  29 -21 0.00
Sat 01/03 17Z 0.84 2821  84  27 -20 0.00
Sat 01/03 18Z 0.63 2821  80  25 -19 0.00
Sat 01/03 19Z 0.55 2822  76  23 -18 0.00
Sat 01/03 20Z 0.49 2822  71  27 -16 0.00
Sat 01/03 21Z 0.41 2922  65  30 -14 0.00
Sat 01/03 22Z 0.38 2921  61  26 -14 0.00
Sat 01/03 23Z 0.37 2921  59  21 -13 0.00
Sun 01/04 00Z 0.35 2920  54  17 -13 0.00
Sun 01/04 01Z 0.32 2919  51  15 -12 0.00
Sun 01/04 02Z 0.29 2918  48  12 -11 0.00
Sun 01/04 03Z 0.28 2816  48  13 -11 0.00
Sun 01/04 04Z 0.29 2715  50  30 -12 0.00
Sun 01/04 05Z 0.28 2715  52  65 -12 0.00

Run total areal avg QPF for the greens is: 0.00 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