Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260114_1800
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 01/14 18Z 1.46 2219  82  80  -1 0.00
Wed 01/14 19Z 0.86 2218  84  78  -1 0.00
Wed 01/14 20Z 0.77 2318  86  89  -1 0.00
Wed 01/14 21Z 0.59 2216  87  90  -1 0.00
Wed 01/14 22Z 0.45 2214  89  93  -1 0.00
Wed 01/14 23Z 0.37 2212  90  95  -1 0.00
Thu 01/15 00Z 0.27 2110  93  95  -1 0.00
Thu 01/15 01Z 0.13 1908  96  94  -1 0.01
Thu 01/15 02Z 0.04 1608  98  94  -1 0.02
Thu 01/15 04Z 0.09 1613  98  92   0 0.03
Thu 01/15 05Z 0.04 1614  96  94   0 0.04
Thu 01/15 07Z 0.05 1614  95  95   0 0.02
Thu 01/15 08Z 0.09 1614  97  96   0 0.03
Thu 01/15 09Z 0.08 1714  96  94   0 0.03
Thu 01/15 10Z 0.07 1814  95  93   0 0.03
Thu 01/15 11Z 0.05 1713  94  88   0 0.03
Thu 01/15 12Z 0.04 1713  93  89   0 0.02
Thu 01/15 13Z 0.04 1713  92  91   0 0.02
Thu 01/15 14Z 0.12 1814  96  94  -1 0.01
Thu 01/15 15Z 0.22 2015  98  84  -1 0.00
Thu 01/15 17Z 0.41 2115  98  15  -2 0.00
Thu 01/15 18Z 0.49 2116  98   4  -3 0.01
Thu 01/15 19Z 0.63 2116  97   3  -4 0.01
Thu 01/15 20Z 0.96 2319  98   2  -7 0.01
Thu 01/15 21Z 0.97 2323  95   8 -10 0.01
Thu 01/15 22Z 0.97 2324  90  19 -12 0.01
Thu 01/15 23Z 1.25 2426  84  33 -14 0.03
Fri 01/16 00Z 2.87 2526  84  54 -15 0.02
Fri 01/16 01Z 5.41 2522  83  66 -16 0.01
Fri 01/16 02Z 6.94 2520  82  67 -17 0.00
Fri 01/16 03Z 7.43 2520  81  66 -18 0.01
Fri 01/16 04Z 8.07 2622  84  60 -19 0.00
Fri 01/16 05Z 7.04 2621  84  41 -19 0.00
Fri 01/16 07Z 3.83 2821  81  55 -20 0.00
Fri 01/16 08Z 2.11 2821  83  70 -20 0.00
Fri 01/16 09Z 1.56 2821  84  69 -20 0.00
Fri 01/16 10Z 1.05 2722  85  69 -20 0.00
Fri 01/16 11Z 0.73 2822  86  62 -19 0.00
Fri 01/16 12Z 0.61 2823  84  49 -17 0.00
Fri 01/16 13Z 0.54 2825  74  43 -16 0.00
Fri 01/16 14Z 0.49 2825  64  32 -15 0.00
Fri 01/16 15Z 0.50 2725  54  23 -14 0.01
Fri 01/16 16Z 0.56 2726  47   6 -14 0.00
Fri 01/16 17Z 0.53 2824  41   5 -13 0.00
Fri 01/16 18Z 0.52 2823  38   6 -12 0.00
Fri 01/16 19Z 0.44 2820  36   7 -11 0.00
Fri 01/16 20Z 0.36 2817  35   9 -10 0.00
Fri 01/16 21Z 0.35 2715  36  13 -10 0.00
Fri 01/16 22Z 0.26 2512  33  53  -9 0.00
Fri 01/16 23Z 0.27 2413  34  93  -9 0.00
Sat 01/17 00Z 0.29 2215  37  90  -9 0.00
Sat 01/17 01Z 0.37 2120  45  85  -9 0.00
Sat 01/17 02Z 0.48 2122  67  79 -10 0.00
Sat 01/17 03Z 0.59 2224  81  81 -10 0.00
Sat 01/17 04Z 0.68 2327  88  88 -10 0.00
Sat 01/17 05Z 0.65 2326  85  75 -10 0.00

Run total areal avg QPF for the Central_Greens is: 0.42 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