Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260117_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 01/17 00Z 0.28 2613  60  44 -11 0.00
Sat 01/17 01Z 0.30 2514  55  58 -10 0.00
Sat 01/17 02Z 0.27 2414  52  74 -10 0.00
Sat 01/17 03Z 0.19 2213  51  89  -9 0.00
Sat 01/17 04Z 0.33 2219  59  91 -10 0.00
Sat 01/17 05Z 0.28 2120  78  91 -11 0.00
Sat 01/17 06Z 0.28 2022  81  92 -10 0.01
Sat 01/17 07Z 0.35 2124  89  91 -10 0.00
Sat 01/17 08Z 0.41 2125  91  88 -10 0.01
Sat 01/17 10Z 0.36 2221  91  87  -9 0.02
Sat 01/17 11Z 0.30 2219  91  89  -8 0.01
Sat 01/17 12Z 0.28 2218  92  89  -8 0.01
Sat 01/17 13Z 0.27 2119  92  88  -8 0.00
Sat 01/17 15Z 0.28 2120  93  89  -7 0.00
Sat 01/17 16Z 0.31 2121  94  87  -7 0.00
Sat 01/17 17Z 0.32 2122  94  85  -7 0.00
Sat 01/17 18Z 0.34 2123  95  87  -6 0.01
Sat 01/17 19Z 0.29 2120  95  88  -6 0.01
Sat 01/17 20Z 0.26 2019  95  88  -6 0.02
Sat 01/17 21Z 0.30 2120  95  90  -6 0.03
Sat 01/17 22Z 0.42 2220  95  90  -7 0.04
Sat 01/17 23Z 0.54 2420  95  87  -7 0.05
Sun 01/18 00Z 0.58 2619  94  71  -7 0.04
Sun 01/18 01Z 0.57 2719  92  53  -7 0.04
Sun 01/18 02Z 0.56 2619  87  49  -7 0.01
Sun 01/18 03Z 0.55 2619  82  47  -7 0.00
Sun 01/18 04Z 0.55 2619  80  46  -7 0.00
Sun 01/18 05Z 0.58 2520  82  47  -7 0.00
Sun 01/18 06Z 0.67 2523  89  45  -8 0.00
Sun 01/18 07Z 0.78 2424  90  44  -8 0.00
Sun 01/18 08Z 0.81 2424  89  41  -8 0.00
Sun 01/18 09Z 0.76 2422  93  33  -8 0.00
Sun 01/18 10Z 0.69 2420  91  30  -9 0.00
Sun 01/18 11Z 0.74 2321  91  39  -9 0.00
Sun 01/18 12Z 0.87 2323  92  40 -10 0.00
Sun 01/18 13Z 1.06 2425  96  22 -10 0.00
Sun 01/18 14Z 1.16 2523  96   8 -11 0.00
Sun 01/18 15Z 1.29 2522  93  10 -12 0.01
Sun 01/18 16Z 2.35 2519  92  13 -12 0.02
Sun 01/18 17Z 2.54 2516  93  15 -13 0.01
Sun 01/18 18Z 2.35 2513  89  14 -13 0.00
Sun 01/18 19Z 1.72 2610  87  12 -13 0.00
Sun 01/18 20Z 1.22 2509  86  11 -12 0.00
Sun 01/18 21Z 0.48 2606  84  11 -12 0.00
Sun 01/18 22Z 0.32 2605  84  14 -12 0.00
Sun 01/18 23Z 0.25 2704  85  16 -12 0.00
Mon 01/19 00Z 0.08 3102  85  16 -12 0.00
Mon 01/19 01Z 0.06 3401  86  16 -12 0.00
Mon 01/19 02Z 0.05 1100  87  19 -12 0.00
Mon 01/19 03Z 0.08 2801  88  22 -13 0.00
Mon 01/19 04Z 0.07 3102  89  24 -13 0.00
Mon 01/19 05Z 0.10 3204  91  25 -13 0.00
Mon 01/19 07Z 0.08 3305  94  30 -13 0.00
Mon 01/19 08Z 0.08 3304  95  33 -14 0.00
Mon 01/19 09Z 0.10 3204  95  34 -14 0.00
Mon 01/19 10Z 0.09 3103  94  31 -14 0.00
Mon 01/19 11Z 0.16 2803  94  28 -14 0.00

Run total areal avg QPF for the greens is: 0.35 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