Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260115_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)
=== ===== === ==== ==== === === === ====
Thu 01/15 12Z 0.03 1710  98  90  -1 0.00
Thu 01/15 13Z 0.08 1810  98  89  -1 0.01
Thu 01/15 14Z 0.22 2012  98  89  -2 0.01
Thu 01/15 15Z 0.41 2215  98  87  -2 0.01
Thu 01/15 18Z 0.59 2319  96  41  -4 0.02
Thu 01/15 19Z 0.54 2321  92  12  -5 0.02
Thu 01/15 20Z 0.69 2421  90   4  -8 0.01
Thu 01/15 21Z 0.73 2420  87   7 -10 0.01
Thu 01/15 22Z 1.43 2620  87   6 -12 0.01
Thu 01/15 23Z 2.53 2619  84  19 -13 0.01
Fri 01/16 00Z 2.89 2618  81  33 -14 0.01
Fri 01/16 02Z 3.73 2616  86  44 -15 0.00
Fri 01/16 03Z 3.05 2616  86  44 -16 0.00
Fri 01/16 04Z 2.06 2516  81  56 -16 0.00
Fri 01/16 05Z 2.49 2615  84  66 -17 0.00
Fri 01/16 06Z 2.53 2718  85  70 -18 0.00
Fri 01/16 07Z 3.15 2821  86  58 -19 0.00
Fri 01/16 08Z 4.27 2821  84  58 -20 0.00
Fri 01/16 09Z 1.48 2822  84  75 -20 0.01
Fri 01/16 10Z 1.02 2922  87  72 -19 0.01
Fri 01/16 11Z 0.76 2923  86  62 -19 0.00
Fri 01/16 12Z 0.62 2924  86  67 -18 0.00
Fri 01/16 13Z 0.55 2924  88  55 -17 0.00
Fri 01/16 14Z 0.50 2924  89  24 -16 0.00
Fri 01/16 15Z 0.45 2923  87   7 -15 0.00
Fri 01/16 16Z 0.47 2823  80   9 -14 0.00
Fri 01/16 17Z 0.43 2822  62   7 -13 0.00
Fri 01/16 18Z 0.40 2821  42  11 -12 0.00
Fri 01/16 19Z 0.41 2819  39  14 -11 0.00
Fri 01/16 20Z 0.38 2818  37  12 -11 0.00
Fri 01/16 21Z 0.35 2716  35  16 -10 0.00
Fri 01/16 22Z 0.39 2616  37  32 -10 0.00
Fri 01/16 23Z 0.34 2515  35  72  -9 0.00
Sat 01/17 00Z 0.26 2313  31  93  -8 0.00
Sat 01/17 01Z 0.21 2113  28  91  -8 0.00
Sat 01/17 02Z 0.26 2116  39  95  -9 0.00
Sat 01/17 03Z 0.27 2018  61  94  -8 0.00
Sat 01/17 04Z 0.34 2022  48  96  -8 0.00
Sat 01/17 05Z 0.59 2125  66  86 -11 0.00
Sat 01/17 06Z 0.52 2126  83  87 -10 0.00
Sat 01/17 07Z 0.52 2224  83  86  -9 0.00
Sat 01/17 08Z 0.52 2322  75  60  -9 0.00
Sat 01/17 09Z 0.50 2321  74  52  -9 0.01
Sat 01/17 10Z 0.49 2319  75  45  -9 0.01
Sat 01/17 11Z 0.48 2219  78  49  -9 0.00
Sat 01/17 12Z 0.50 2318  79  65  -9 0.00
Sat 01/17 13Z 0.54 2319  82  79  -9 0.00
Sat 01/17 14Z 0.52 2319  90  83  -9 0.00
Sat 01/17 15Z 0.50 2318  91  84  -9 0.00
Sat 01/17 16Z 0.48 2316  90  75  -9 0.00
Sat 01/17 17Z 0.55 2316  92  55  -9 0.00
Sat 01/17 18Z 0.59 2317  92  56  -9 0.01
Sat 01/17 19Z 0.60 2316  90  57  -9 0.00
Sat 01/17 21Z 0.60 2215  89  71  -8 0.00

Run total areal avg QPF for the Central_Greens is: 0.17 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