NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260526_0000
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)
=== ===== === ==== ==== === === === ====
Tue 05/26 00Z 0.50 2914  77   2   9 0.00
Tue 05/26 01Z 0.76 2917  72   2   9 0.00
Tue 05/26 02Z 0.67 3018  70   4   9 0.00
Tue 05/26 03Z 0.53 3017  67   6   9 0.00
Tue 05/26 04Z 0.41 3118  66   7   9 0.00
Tue 05/26 05Z 0.42 3119  65   8   9 0.00
Tue 05/26 06Z 0.55 3019  65   9   9 0.00
Tue 05/26 07Z 0.60 3019  68   9   9 0.00
Tue 05/26 08Z 0.55 3020  74   9   9 0.00
Tue 05/26 09Z 0.46 3019  78  11  10 0.00
Tue 05/26 10Z 0.38 3017  79  12  10 0.00
Tue 05/26 11Z 0.35 3015  76  13  10 0.00
Tue 05/26 12Z 0.33 3015  75  19  10 0.00
Tue 05/26 13Z 0.31 3012  73  17  11 0.00
Tue 05/26 14Z 0.35 2911  76  39  11 0.00
Tue 05/26 15Z 0.48 2812  78  60  11 0.00
Tue 05/26 16Z 0.65 2812  76  58  11 0.00
Tue 05/26 17Z 1.47 2712  74  49  12 0.00
Tue 05/26 18Z 1.47 2711  77  33  12 0.00
Tue 05/26 19Z 3.01 2512  79  34  12 0.00
Tue 05/26 20Z 4.41 2415  81  34  12 0.00
Tue 05/26 21Z 3.59 2318  83  32  12 0.00
Tue 05/26 22Z 2.69 2422  80  23  12 0.01
Tue 05/26 23Z 1.56 2425  72  26  13 0.00
Wed 05/27 00Z 1.56 2428  71  31  13 0.00
Wed 05/27 01Z 1.67 2431  72  38  12 0.00
Wed 05/27 02Z 1.33 2532  67  41  13 0.00
Wed 05/27 03Z 1.26 2532  63  48  13 0.00
Wed 05/27 04Z 1.19 2631  60  58  13 0.00
Wed 05/27 05Z 1.20 2630  61  58  12 0.00
Wed 05/27 06Z 1.17 2729  62  53  12 0.00
Wed 05/27 07Z 1.09 2828  65  46  12 0.00
Wed 05/27 08Z 0.91 2926  74  55  11 0.00
Wed 05/27 09Z 0.73 2923  84  54  11 0.00
Wed 05/27 10Z 0.66 2922  87  54  11 0.00
Wed 05/27 11Z 0.60 2920  88  60  11 0.00
Wed 05/27 12Z 0.54 2817  88  58  11 0.00
Wed 05/27 13Z 0.53 2815  90  58  11 0.00
Wed 05/27 14Z 0.54 2813  92  45  11 0.00
Wed 05/27 15Z 0.68 2812  93  35  11 0.00
Wed 05/27 16Z 0.83 2910  94  31  10 0.00
Wed 05/27 17Z 1.19 3012  94  32  10 0.01
Wed 05/27 18Z 0.34 3115  92  30  10 0.04
Wed 05/27 19Z 0.69 3215  85  30  10 0.00
Wed 05/27 20Z 1.75 3215  79  26  10 0.00
Wed 05/27 21Z 2.38 3215  77  23   9 0.00
Wed 05/27 22Z 1.46 3316  76  18   9 0.00
Wed 05/27 23Z 0.68 3318  74  14   8 0.00
Thu 05/28 00Z 0.42 3320  74  13   7 0.00
Thu 05/28 01Z 0.31 3321  77   9   7 0.00
Thu 05/28 02Z 0.21 3321  81   9   6 0.00
Thu 05/28 03Z 0.12 3420  85   7   6 0.00
Thu 05/28 04Z 0.05 3420  90   8   6 0.00
Thu 05/28 05Z 0.04 3518  93  18   5 0.00
Thu 05/28 06Z 0.03 3517  94  21   5 0.00
Thu 05/28 07Z 0.04 3416  93  25   5 0.00
Thu 05/28 08Z 0.05 3416  92  27   5 0.00
Thu 05/28 09Z 0.06 3416  91  31   5 0.00
Thu 05/28 10Z 0.05 3417  91  36   5 0.00
Thu 05/28 11Z 0.03 3417  93  42   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.06 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