NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260301_1200
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)
=== ===== === ==== ==== === === === ====
Sun 03/01 12Z 0.26 3214  85  86 -13 0.00
Sun 03/01 13Z 0.27 3217  83  67 -13 0.00
Sun 03/01 14Z 0.29 3117  76  43 -14 0.00
Sun 03/01 15Z 0.38 3118  75  37 -15 0.00
Sun 03/01 16Z 0.42 3119  75  34 -15 0.00
Sun 03/01 17Z 0.47 3120  73  26 -16 0.00
Sun 03/01 19Z 0.63 3119  74  28 -17 0.00
Sun 03/01 20Z 0.67 3120  76  36 -18 0.00
Sun 03/01 21Z 0.69 3020  76  43 -18 0.00
Sun 03/01 22Z 0.67 3021  75  46 -18 0.00
Sun 03/01 23Z 0.64 3022  73  49 -19 0.00
Mon 03/02 00Z 0.63 3022  70  43 -19 0.00
Mon 03/02 01Z 0.57 3023  63  34 -20 0.00
Mon 03/02 02Z 0.47 3122  55  25 -20 0.00
Mon 03/02 03Z 0.40 3121  50  20 -20 0.00
Mon 03/02 04Z 0.37 3121  48  17 -20 0.00
Mon 03/02 05Z 0.36 3120  45  14 -20 0.00
Mon 03/02 06Z 0.34 3119  43  12 -20 0.00
Mon 03/02 07Z 0.34 3019  42  10 -20 0.00
Mon 03/02 08Z 0.35 3019  40   9 -20 0.00
Mon 03/02 09Z 0.35 3019  41   9 -20 0.00
Mon 03/02 10Z 0.36 3019  42  10 -20 0.00
Mon 03/02 11Z 0.37 3019  45  11 -20 0.00
Mon 03/02 13Z 0.41 2920  51  17 -20 0.00
Mon 03/02 14Z 0.41 2919  51  19 -20 0.00
Mon 03/02 15Z 0.41 2918  50  20 -19 0.00
Mon 03/02 16Z 0.44 2917  45  21 -19 0.00
Mon 03/02 17Z 0.46 2917  41  19 -18 0.00
Mon 03/02 18Z 0.44 2916  40  17 -18 0.00
Mon 03/02 19Z 0.42 2815  41  16 -17 0.00
Mon 03/02 20Z 0.38 2813  41  13 -16 0.00
Mon 03/02 21Z 0.38 2713  40  10 -15 0.00
Mon 03/02 22Z 0.38 2714  40  13 -14 0.00
Mon 03/02 23Z 0.38 2615  40  28 -13 0.00
Tue 03/03 00Z 0.37 2516  40  53 -12 0.00
Tue 03/03 01Z 0.39 2419  37  60 -11 0.00
Tue 03/03 02Z 0.44 2422  34  70 -10 0.00
Tue 03/03 03Z 0.51 2425  29  67 -10 0.00
Tue 03/03 04Z 0.56 2428  27  66  -9 0.00
Tue 03/03 05Z 0.60 2530  25  65  -8 0.00
Tue 03/03 06Z 0.61 2530  22  65  -7 0.00
Tue 03/03 07Z 0.60 2530  23  64  -6 0.00
Tue 03/03 08Z 0.58 2528  24  62  -5 0.00
Tue 03/03 09Z 0.56 2527  24  59  -5 0.00
Tue 03/03 10Z 0.56 2527  25  54  -4 0.00
Tue 03/03 11Z 0.56 2526  25  51  -4 0.00
Tue 03/03 12Z 0.53 2525  25  44  -4 0.00
Tue 03/03 13Z 0.49 2524  28  38  -4 0.00
Tue 03/03 14Z 0.44 2423  32  31  -3 0.00
Tue 03/03 15Z 0.43 2423  39  24  -3 0.00
Tue 03/03 16Z 0.42 2324  48  19  -3 0.00
Tue 03/03 17Z 0.42 2324  60  15  -3 0.00
Tue 03/03 18Z 0.43 2324  71  15  -3 0.00
Tue 03/03 19Z 0.42 2323  77  16  -3 0.00
Tue 03/03 20Z 0.40 2322  81  28  -2 0.00
Tue 03/03 21Z 0.36 2320  82  33  -2 0.00
Tue 03/03 22Z 0.32 2318  84  51  -1 0.01
Tue 03/03 23Z 0.28 2317  85  75  -1 0.01

Run total areal avg QPF for the greens is: 0.02 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