NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260225_1200
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)
=== ===== === ==== ==== === === === ====
Wed 02/25 12Z 0.28 1928  90  85 -10 0.00
Wed 02/25 13Z 0.35 2027  94  86 -10 0.01
Wed 02/25 14Z 0.45 2125  96  90 -10 0.01
Wed 02/25 15Z 0.51 2222  95  86  -9 0.01
Wed 02/25 16Z 0.57 2220  95  77  -9 0.00
Wed 02/25 17Z 0.70 2218  92  67  -8 0.00
Wed 02/25 18Z 1.45 2117  90  50  -8 0.00
Wed 02/25 19Z 4.88 2216  86  34  -7 0.00
Wed 02/25 20Z 5.55 2317  86  43  -7 0.00
Wed 02/25 21Z 1.55 2216  87  68  -7 0.00
Wed 02/25 22Z 0.76 2117  87  63  -6 0.00
Wed 02/25 23Z 0.55 2020  88  67  -6 0.00
Thu 02/26 00Z 0.53 2023  90  82  -5 0.00
Thu 02/26 01Z 0.65 2126  94  83  -5 0.00
Thu 02/26 02Z 0.79 2229  96  82  -5 0.01
Thu 02/26 03Z 1.07 2328  97  86  -5 0.02
Thu 02/26 04Z 1.37 2424  93  86  -7 0.02
Thu 02/26 05Z 1.06 2522  94  38  -7 0.01
Thu 02/26 07Z 1.46 2626  89  13  -9 0.02
Thu 02/26 08Z 1.44 2628  81  16 -11 0.02
Thu 02/26 09Z 1.55 2730  75  22 -12 0.00
Thu 02/26 10Z 1.29 2731  69  18 -13 0.00
Thu 02/26 11Z 1.13 2732  65  16 -13 0.00
Thu 02/26 12Z 1.01 2832  66   4 -13 0.00
Thu 02/26 13Z 1.06 2730  67   4 -14 0.00
Thu 02/26 14Z 1.39 2726  69   1 -15 0.00
Thu 02/26 15Z 2.92 2724  70   2 -15 0.00
Thu 02/26 16Z 2.38 2820  70   4 -14 0.00
Thu 02/26 17Z 4.47 2719  73   6 -14 0.00
Thu 02/26 18Z 8.81 2718  75   9 -14 0.00
Thu 02/26 19Z 8.35 2616  75  13 -14 0.00
Thu 02/26 20Z 7.59 2616  75  18 -13 0.00
Thu 02/26 21Z 5.47 2716  74  22 -13 0.00
Thu 02/26 22Z 2.44 2717  74  27 -13 0.00
Thu 02/26 23Z 1.77 2719  74  33 -13 0.00
Fri 02/27 00Z 1.28 2721  73  39 -13 0.00
Fri 02/27 01Z 0.96 2822  71  45 -14 0.00
Fri 02/27 02Z 0.69 2821  67  47 -14 0.00
Fri 02/27 03Z 0.52 2920  66  46 -13 0.00
Fri 02/27 04Z 0.42 2919  68  48 -13 0.00
Fri 02/27 05Z 0.37 2918  69  42 -13 0.00
Fri 02/27 06Z 0.32 2917  68  43 -12 0.00
Fri 02/27 07Z 0.29 2916  64  47 -11 0.00
Fri 02/27 08Z 0.27 2916  60  59 -11 0.00
Fri 02/27 09Z 0.28 2916  59  60 -10 0.00
Fri 02/27 10Z 0.32 2817  61  65 -10 0.00
Fri 02/27 11Z 0.32 2817  60  76 -10 0.00
Fri 02/27 12Z 0.34 2717  65  84  -9 0.00
Fri 02/27 13Z 0.37 2619  71  86  -8 0.00
Fri 02/27 14Z 0.42 2520  77  82  -8 0.00
Fri 02/27 15Z 0.47 2521  73  80  -7 0.00
Fri 02/27 17Z 0.52 2421  63  89  -5 0.00
Fri 02/27 18Z 0.55 2323  61  71  -5 0.00
Fri 02/27 19Z 0.64 2326  60  78  -5 0.00
Fri 02/27 20Z 0.72 2327  56  62  -4 0.00
Fri 02/27 21Z 0.85 2329  59  66  -4 0.00
Fri 02/27 22Z 0.90 2330  65  70  -4 0.00
Fri 02/27 23Z 0.85 2330  71  58  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.13 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