NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260328_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 03/28 06Z 0.17 3312  80  13 -15 0.00
Sat 03/28 07Z 0.27 3214  79  17 -15 0.00
Sat 03/28 08Z 0.31 3213  79  18 -16 0.00
Sat 03/28 09Z 0.44 3213  82  37 -16 0.00
Sat 03/28 10Z 0.55 3214  85  46 -17 0.00
Sat 03/28 11Z 0.49 3214  86  56 -17 0.00
Sat 03/28 12Z 0.52 3111  86  62 -17 0.00
Sat 03/28 13Z 1.36 3110  84  59 -17 0.00
Sat 03/28 14Z 2.44 3009  79  59 -16 0.00
Sat 03/28 15Z 3.33 3009  73  57 -16 0.00
Sat 03/28 16Z 4.71 2910  71  56 -15 0.00
Sat 03/28 17Z 7.14 2711  72  60 -15 0.00
Sat 03/28 18Z 8.98 2613  71  66 -14 0.00
Sat 03/28 19Z 9.68 2715  72  71 -13 0.00
Sat 03/28 20Z 7.47 2718  78  68 -13 0.00
Sat 03/28 21Z 11.15 2819  67  49 -13 0.00
Sat 03/28 22Z 8.54 2819  71  60 -13 0.00
Sat 03/28 23Z 3.91 2720  82  56 -14 0.00
Sun 03/29 00Z 5.16 2825  83  55 -14 0.01
Sun 03/29 01Z 4.17 2926  75  41 -14 0.00
Sun 03/29 02Z 1.93 2824  71  24 -14 0.00
Sun 03/29 03Z 1.82 2823  70  10 -14 0.00
Sun 03/29 04Z 1.68 2823  77  21 -14 0.00
Sun 03/29 05Z 1.52 2824  85  63 -14 0.00
Sun 03/29 06Z 1.32 2823  88  76 -14 0.00
Sun 03/29 07Z 1.21 2823  90  73 -14 0.00
Sun 03/29 08Z 1.10 2823  91  78 -14 0.00
Sun 03/29 09Z 1.01 2822  92  74 -13 0.00
Sun 03/29 10Z 0.93 2722  92  74 -13 0.00
Sun 03/29 11Z 0.78 2720  92  70 -12 0.00
Sun 03/29 12Z 0.75 2621  91  77 -12 0.00
Sun 03/29 13Z 0.75 2621  85  80 -11 0.00
Sun 03/29 14Z 0.77 2621  84  77 -10 0.00
Sun 03/29 15Z 0.90 2619  78  78  -9 0.00
Sun 03/29 16Z 0.92 2418  66  85  -8 0.00
Sun 03/29 17Z 1.56 2320  58  89  -8 0.00
Sun 03/29 18Z 1.64 2321  55  79  -7 0.00
Sun 03/29 19Z 2.89 2323  54  76  -7 0.00
Sun 03/29 20Z 3.45 2324  54  56  -6 0.00
Sun 03/29 21Z 1.75 2325  56  74  -5 0.00
Sun 03/29 22Z 1.37 2427  56  43  -4 0.00
Sun 03/29 23Z 1.42 2429  55  24  -4 0.00
Mon 03/30 00Z 1.40 2430  53   9  -3 0.00
Mon 03/30 01Z 1.42 2430  52   6  -3 0.00
Mon 03/30 02Z 1.61 2532  51   9  -2 0.00
Mon 03/30 03Z 1.68 2532  55  16  -2 0.00
Mon 03/30 04Z 1.29 2529  54  48  -2 0.00
Mon 03/30 05Z 1.15 2528  59  84  -2 0.00
Mon 03/30 06Z 0.95 2428  69  82  -1 0.00
Mon 03/30 07Z 0.92 2526  66  85  -1 0.00
Mon 03/30 08Z 0.81 2426  77  61  -1 0.00
Mon 03/30 09Z 0.79 2426  82  56  -2 0.00
Mon 03/30 10Z 0.81 2526  84  68  -2 0.00
Mon 03/30 11Z 0.85 2526  84  84  -2 0.00
Mon 03/30 12Z 0.84 2525  80  93  -2 0.00
Mon 03/30 13Z 0.85 2526  84  88  -2 0.00
Mon 03/30 14Z 0.91 2526  82  70  -1 0.00
Mon 03/30 15Z 0.90 2525  67  75   0 0.00
Mon 03/30 16Z 1.04 2526  69  81   0 0.00
Mon 03/30 17Z 1.19 2525  68  78   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.01 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