NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260102_0000
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)
=== ===== === ==== ==== === === === ====
Fri 01/02 00Z 1.02 2821  76  23 -21 0.00
Fri 01/02 01Z 1.10 2826  73  15 -21 0.00
Fri 01/02 02Z 0.92 2926  67  11 -21 0.00
Fri 01/02 03Z 0.86 2926  66  14 -21 0.00
Fri 01/02 04Z 0.89 2926  68  24 -21 0.00
Fri 01/02 05Z 0.82 2926  77  38 -20 0.00
Fri 01/02 06Z 0.72 2823  81  56 -20 0.00
Fri 01/02 07Z 0.67 2721  81  60 -19 0.00
Fri 01/02 08Z 0.59 2719  85  67 -19 0.00
Fri 01/02 09Z 0.58 2618  88  74 -19 0.00
Fri 01/02 10Z 0.64 2619  90  73 -19 0.00
Fri 01/02 11Z 0.64 2619  92  71 -18 0.00
Fri 01/02 12Z 0.65 2619  92  62 -18 0.00
Fri 01/02 13Z 0.67 2620  91  56 -18 0.00
Fri 01/02 14Z 0.75 2621  91  55 -18 0.00
Fri 01/02 15Z 0.89 2720  89  42 -18 0.00
Fri 01/02 16Z 1.15 2719  86  46 -18 0.00
Fri 01/02 17Z 2.91 2718  86  48 -18 0.00
Fri 01/02 18Z 5.46 2718  87  40 -18 0.00
Fri 01/02 19Z 5.80 2718  87  33 -18 0.00
Fri 01/02 20Z 4.01 2719  89  28 -17 0.00
Fri 01/02 21Z 2.54 2720  88  22 -17 0.00
Fri 01/02 22Z 1.76 2722  88  20 -17 0.00
Fri 01/02 23Z 1.72 2824  86  28 -18 0.00
Sat 01/03 00Z 1.70 2826  84  46 -18 0.00
Sat 01/03 01Z 1.34 2826  85  64 -18 0.00
Sat 01/03 02Z 1.31 2825  88  73 -18 0.00
Sat 01/03 03Z 1.39 2825  90  70 -18 0.00
Sat 01/03 04Z 1.43 2825  90  70 -19 0.00
Sat 01/03 05Z 1.70 2826  86  75 -19 0.00
Sat 01/03 06Z 1.88 2826  84  76 -19 0.00
Sat 01/03 07Z 1.45 2827  84  75 -19 0.00
Sat 01/03 08Z 1.75 2827  87  75 -20 0.00
Sat 01/03 09Z 1.72 2827  88  72 -20 0.00
Sat 01/03 10Z 1.34 2828  88  61 -20 0.00
Sat 01/03 11Z 1.18 2830  88  49 -20 0.00
Sat 01/03 12Z 1.12 2830  89  45 -20 0.00
Sat 01/03 13Z 1.04 2929  91  38 -20 0.00
Sat 01/03 14Z 1.11 2927  91  30 -20 0.00
Sat 01/03 15Z 1.93 2924  90  31 -21 0.00
Sat 01/03 16Z 1.99 2822  90  33 -21 0.00
Sat 01/03 17Z 1.23 2821  88  34 -20 0.00
Sat 01/03 18Z 0.97 2820  86  31 -19 0.00
Sat 01/03 19Z 0.72 2721  82  29 -18 0.00
Sat 01/03 20Z 0.59 2722  77  28 -16 0.00
Sat 01/03 21Z 0.59 2723  74  25 -15 0.00
Sat 01/03 22Z 0.57 2823  71  24 -15 0.00
Sat 01/03 23Z 0.51 2822  68  25 -14 0.00
Sun 01/04 00Z 0.46 2821  68  32 -13 0.00
Sun 01/04 01Z 0.45 2821  70  59 -13 0.00
Sun 01/04 02Z 0.45 2820  74  76 -13 0.00
Sun 01/04 03Z 0.51 2720  80  86 -14 0.00
Sun 01/04 04Z 0.53 2719  85  86 -15 0.00
Sun 01/04 05Z 0.56 2719  87  85 -15 0.01
Sun 01/04 06Z 0.56 2719  87  84 -15 0.02
Sun 01/04 07Z 0.58 2719  88  84 -15 0.02
Sun 01/04 08Z 0.60 2720  88  84 -15 0.02
Sun 01/04 09Z 0.61 2720  89  84 -15 0.01
Sun 01/04 10Z 0.58 2819  89  83 -15 0.01
Sun 01/04 11Z 0.56 2819  90  81 -15 0.01

Run total areal avg QPF for the greens is: 0.10 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