Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260615_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)
=== ===== === ==== ==== === === === ====
Mon 06/15 00Z 0.82 2029  71  93  15 0.00
Mon 06/15 01Z 0.66 2028  72  90  15 0.01
Mon 06/15 02Z 0.52 2026  81  94  15 0.01
Mon 06/15 03Z 0.36 1924  86  84  15 0.03
Mon 06/15 04Z 0.47 2615  97  92  12 0.45
Mon 06/15 05Z 0.39 2514  93  87  12 0.33
Mon 06/15 06Z 0.35 2512  93  96  12 0.08
Mon 06/15 07Z 0.31 2710  97  99  11 0.16
Mon 06/15 08Z 0.35 2913  97  98  11 0.08
Mon 06/15 09Z 0.50 2917  97  98  10 0.07
Mon 06/15 10Z 0.43 3121  97  91   9 0.03
Mon 06/15 11Z 0.33 3121  92  84   9 0.01
Mon 06/15 12Z 0.38 3121  84  56   9 0.00
Mon 06/15 13Z 0.47 3021  80  39   8 0.00
Mon 06/15 14Z 0.53 3019  79  16   8 0.00
Mon 06/15 15Z 1.02 3017  83  10   7 0.00
Mon 06/15 16Z 4.14 2916  86  19   7 0.00
Mon 06/15 17Z 5.47 3015  86  18   7 0.00
Mon 06/15 18Z 4.08 3114  84  13   7 0.00
Mon 06/15 19Z 4.00 3113  81   8   7 0.00
Mon 06/15 20Z 3.92 3014  81   6   7 0.00
Mon 06/15 21Z 4.12 3014  83   6   7 0.00
Mon 06/15 22Z 2.62 3115  84   7   7 0.00
Mon 06/15 23Z 0.90 3115  84   8   6 0.00
Tue 06/16 00Z 0.49 3115  87   9   6 0.00
Tue 06/16 01Z 0.48 3016  90   9   6 0.00
Tue 06/16 02Z 0.50 3017  92   9   6 0.00
Tue 06/16 03Z 0.48 3018  95  12   5 0.00
Tue 06/16 04Z 0.43 3118  96  19   5 0.01
Tue 06/16 05Z 0.40 3118  96  24   4 0.01
Tue 06/16 06Z 0.37 3119  96  19   4 0.01
Tue 06/16 07Z 0.38 3120  96   9   4 0.01
Tue 06/16 08Z 0.34 3119  94   3   4 0.01
Tue 06/16 09Z 0.30 3218  92   2   4 0.01
Tue 06/16 10Z 0.25 3217  89   3   5 0.00
Tue 06/16 11Z 0.21 3216  83   8   5 0.00
Tue 06/16 12Z 0.17 3215  76  16   6 0.00
Tue 06/16 13Z 0.15 3213  69  26   7 0.00
Tue 06/16 14Z 0.14 3212  64  28   7 0.00
Tue 06/16 15Z 0.20 3209  63  30   7 0.00
Tue 06/16 16Z 0.83 3107  61  26   7 0.00
Tue 06/16 17Z 2.23 2906  57  30   8 0.00
Tue 06/16 18Z 3.24 2706  55  42   8 0.00
Tue 06/16 19Z 4.27 2607  58  39   9 0.00
Tue 06/16 20Z 3.92 2507  59  36   9 0.00
Tue 06/16 21Z 3.77 2407  61  25   9 0.00
Tue 06/16 22Z 2.73 2308  64  19   9 0.00
Tue 06/16 23Z 1.09 2310  66   8   9 0.00
Wed 06/17 00Z 0.82 2312  67  15   9 0.00
Wed 06/17 01Z 0.91 2315  70  22   9 0.00
Wed 06/17 02Z 1.00 2416  71  21   9 0.00
Wed 06/17 03Z 0.96 2416  71  31   9 0.00
Wed 06/17 04Z 0.85 2516  75  25   9 0.00
Wed 06/17 05Z 0.80 2515  77  33   8 0.00
Wed 06/17 06Z 0.70 2414  78  32   8 0.00
Wed 06/17 07Z 0.67 2413  79  30   8 0.00
Wed 06/17 08Z 0.58 2411  81  24   8 0.00
Wed 06/17 09Z 0.58 2312  83  30   8 0.00
Wed 06/17 10Z 0.54 2212  82  28   8 0.00
Wed 06/17 11Z 0.37 2109  80  21   8 0.00

Run total areal avg QPF for the Central_Greens is: 1.32 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