NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260101_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)
=== ===== === ==== ==== === === === ====
Thu 01/01 12Z 1.06 2720  89  70 -16 0.00
Thu 01/01 13Z 2.82 2821  90  61 -17 0.00
Thu 01/01 14Z 4.48 2923  87  54 -18 0.01
Thu 01/01 15Z 4.04 2921  87  55 -19 0.01
Thu 01/01 16Z 3.70 2921  88  61 -19 0.00
Thu 01/01 17Z 3.73 2920  86  57 -20 0.00
Thu 01/01 18Z 5.86 2820  84  51 -20 0.00
Thu 01/01 19Z 5.92 2821  81  39 -20 0.00
Thu 01/01 20Z 4.26 2820  78  39 -20 0.00
Thu 01/01 21Z 2.89 2821  78  47 -20 0.00
Thu 01/01 22Z 1.79 2823  72  34 -21 0.00
Thu 01/01 23Z 1.26 2825  62  13 -21 0.00
Fri 01/02 00Z 0.93 2927  50   9 -20 0.00
Fri 01/02 01Z 0.86 2927  53   8 -20 0.00
Fri 01/02 02Z 0.73 2925  58  12 -20 0.00
Fri 01/02 03Z 0.67 2922  65  23 -19 0.00
Fri 01/02 04Z 0.65 2821  71  43 -19 0.00
Fri 01/02 05Z 0.70 2720  78  62 -19 0.00
Fri 01/02 06Z 0.79 2621  85  67 -19 0.00
Fri 01/02 07Z 0.75 2620  86  66 -19 0.00
Fri 01/02 08Z 0.80 2620  89  67 -19 0.00
Fri 01/02 09Z 0.81 2620  91  69 -19 0.00
Fri 01/02 10Z 0.76 2619  91  65 -19 0.00
Fri 01/02 11Z 0.72 2718  89  61 -19 0.00
Fri 01/02 12Z 0.73 2718  86  60 -19 0.00
Fri 01/02 13Z 0.75 2718  85  49 -19 0.00
Fri 01/02 14Z 0.81 2618  84  44 -19 0.00
Fri 01/02 15Z 1.13 2618  84  39 -19 0.00
Fri 01/02 16Z 4.02 2618  79  39 -19 0.00
Fri 01/02 17Z 7.85 2617  79  38 -19 0.00
Fri 01/02 18Z 9.43 2716  81  31 -18 0.00
Fri 01/02 19Z 9.11 2716  79  25 -18 0.00
Fri 01/02 20Z 5.66 2716  79  21 -18 0.00
Fri 01/02 21Z 1.71 2617  80  21 -17 0.00
Fri 01/02 22Z 1.77 2620  81  20 -17 0.00
Fri 01/02 23Z 2.26 2722  78  22 -17 0.00
Sat 01/03 00Z 1.89 2723  79  40 -18 0.00
Sat 01/03 01Z 1.73 2725  82  62 -18 0.00
Sat 01/03 02Z 1.54 2827  82  75 -17 0.00
Sat 01/03 03Z 1.40 2828  85  73 -17 0.00
Sat 01/03 04Z 1.57 2829  88  69 -18 0.00
Sat 01/03 05Z 2.10 2829  87  68 -18 0.00
Sat 01/03 06Z 2.04 2829  86  71 -19 0.00
Sat 01/03 07Z 1.66 2828  85  71 -19 0.00
Sat 01/03 08Z 1.90 2928  87  62 -20 0.00
Sat 01/03 09Z 1.70 2928  87  50 -20 0.00
Sat 01/03 10Z 1.03 2927  86  47 -20 0.00
Sat 01/03 11Z 0.86 2926  88  42 -19 0.00
Sat 01/03 12Z 0.79 2825  91  36 -19 0.00
Sat 01/03 13Z 0.88 2824  93  34 -19 0.00
Sat 01/03 14Z 1.20 2823  94  41 -20 0.01
Sat 01/03 15Z 1.53 2822  93  52 -20 0.00
Sat 01/03 16Z 1.51 2822  92  58 -19 0.00
Sat 01/03 17Z 1.21 2722  92  61 -19 0.00
Sat 01/03 18Z 0.96 2723  91  66 -18 0.00
Sat 01/03 19Z 0.83 2723  90  65 -17 0.00
Sat 01/03 20Z 0.78 2723  89  55 -16 0.00
Sat 01/03 21Z 0.78 2723  89  43 -16 0.00
Sat 01/03 22Z 0.83 2723  88  33 -16 0.00
Sat 01/03 23Z 0.79 2824  85  25 -16 0.00

Run total areal avg QPF for the greens is: 0.03 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