NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260328_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)
=== ===== === ==== ==== === === === ====
Sat 03/28 12Z 0.37 3009  81  61 -16 0.00
Sat 03/28 13Z 0.73 2910  80  67 -16 0.00
Sat 03/28 14Z 2.27 2909  79  62 -16 0.00
Sat 03/28 15Z 3.94 2808  75  59 -16 0.00
Sat 03/28 16Z 4.85 2808  68  67 -15 0.00
Sat 03/28 17Z 5.66 2709  64  70 -14 0.00
Sat 03/28 18Z 6.36 2510  65  76 -14 0.00
Sat 03/28 19Z 5.07 2513  78  80 -13 0.00
Sat 03/28 20Z 5.66 2716  81  79 -13 0.01
Sat 03/28 21Z 8.44 2718  73  65 -13 0.01
Sat 03/28 22Z 6.91 2720  78  59 -13 0.00
Sat 03/28 23Z 3.88 2722  83  54 -13 0.01
Sun 03/29 00Z 3.14 2723  85  50 -14 0.01
Sun 03/29 01Z 5.34 2824  81  40 -14 0.00
Sun 03/29 02Z 5.22 2825  80  31 -14 0.00
Sun 03/29 03Z 2.57 2824  74  18 -14 0.00
Sun 03/29 04Z 2.00 2824  70  20 -14 0.00
Sun 03/29 05Z 1.86 2823  73  42 -14 0.00
Sun 03/29 06Z 1.89 2823  80  64 -14 0.00
Sun 03/29 07Z 1.61 2723  84  69 -14 0.00
Sun 03/29 08Z 1.32 2822  85  71 -14 0.00
Sun 03/29 09Z 1.17 2822  89  80 -13 0.00
Sun 03/29 10Z 1.04 2722  92  80 -13 0.00
Sun 03/29 11Z 0.95 2721  92  81 -13 0.00
Sun 03/29 12Z 0.82 2721  89  78 -12 0.00
Sun 03/29 13Z 0.78 2621  87  75 -11 0.00
Sun 03/29 14Z 0.86 2620  88  80 -11 0.00
Sun 03/29 15Z 0.97 2519  82  76 -10 0.00
Sun 03/29 16Z 1.17 2517  74  73  -9 0.00
Sun 03/29 17Z 1.78 2416  68  80  -8 0.00
Sun 03/29 18Z 3.99 2316  66  78  -8 0.00
Sun 03/29 19Z 6.29 2318  66  73  -8 0.00
Sun 03/29 20Z 4.67 2320  65  63  -7 0.00
Sun 03/29 21Z 1.67 2322  63  47  -6 0.00
Sun 03/29 22Z 1.24 2324  64  33  -5 0.00
Sun 03/29 23Z 1.28 2426  68  25  -5 0.00
Mon 03/30 00Z 1.42 2426  69   9  -4 0.00
Mon 03/30 01Z 1.28 2527  68   9  -4 0.00
Mon 03/30 02Z 1.24 2527  64   6  -3 0.00
Mon 03/30 03Z 1.21 2527  61   6  -3 0.00
Mon 03/30 04Z 1.13 2527  60  12  -3 0.00
Mon 03/30 05Z 1.01 2526  60  25  -2 0.00
Mon 03/30 06Z 0.96 2527  62  46  -2 0.00
Mon 03/30 07Z 0.88 2427  62  66  -1 0.00
Mon 03/30 08Z 0.89 2425  68  64  -1 0.00
Mon 03/30 09Z 0.92 2425  74  78  -1 0.00
Mon 03/30 10Z 0.71 2423  77  73  -1 0.00
Mon 03/30 11Z 0.68 2424  77  57  -1 0.00
Mon 03/30 12Z 0.78 2426  84  40  -1 0.00
Mon 03/30 13Z 0.82 2526  85  58  -1 0.00
Mon 03/30 14Z 0.85 2527  88  81  -1 0.00
Mon 03/30 15Z 0.89 2527  84  80  -1 0.00
Mon 03/30 16Z 0.88 2627  77  79   0 0.00
Mon 03/30 17Z 0.93 2625  79  69   0 0.00
Mon 03/30 18Z 1.04 2623  80  66   0 0.00
Mon 03/30 19Z 1.08 2522  81  56   0 0.00
Mon 03/30 20Z 1.20 2523  82  59   1 0.00
Mon 03/30 21Z 1.25 2424  82  61   1 0.00
Mon 03/30 22Z 1.32 2526  82  61   1 0.00
Mon 03/30 23Z 1.53 2527  83  61   1 0.00

Run total areal avg QPF for the greens is: 0.04 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