Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260625_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)
=== ===== === ==== ==== === === === ====
Thu 06/25 18Z 4.17 2208  78  36  11 0.00
Thu 06/25 19Z 4.01 2209  79  37  11 0.00
Thu 06/25 20Z 4.08 2311  77  43  11 0.02
Thu 06/25 21Z 2.68 2211  74  47  11 0.01
Thu 06/25 22Z 0.81 2211  72  50  11 0.01
Thu 06/25 23Z 0.47 2209  67  59  12 0.00
Fri 06/26 00Z 0.38 2109  66  84  12 0.00
Fri 06/26 01Z 0.33 2009  66  94  11 0.00
Fri 06/26 02Z 0.26 1810  71  98  11 0.00
Fri 06/26 03Z 0.09 1710  83  97  10 0.02
Fri 06/26 04Z 0.08 1714  90  96  10 0.04
Fri 06/26 05Z 0.13 1715  94  95  10 0.07
Fri 06/26 06Z 0.16 1818  96  93  10 0.10
Fri 06/26 07Z 0.10 1719  96  86  10 0.14
Fri 06/26 08Z 0.09 1718  98  86  10 0.08
Fri 06/26 09Z 0.17 1818  97  85  10 0.03
Fri 06/26 10Z 0.23 1920  98  83  10 0.02
Fri 06/26 11Z 0.37 2019  99  85  10 0.04
Fri 06/26 12Z 0.45 2218  97  73  10 0.04
Fri 06/26 13Z 0.50 2317  94  66  11 0.02
Fri 06/26 14Z 0.49 2215  97  60  10 0.01
Fri 06/26 15Z 0.45 2313  99  57  11 0.01
Fri 06/26 16Z 0.45 2411  98  59  11 0.01
Fri 06/26 17Z 0.51 2510  96  63  11 0.01
Fri 06/26 18Z 0.54 2509  95  58  11 0.00
Fri 06/26 19Z 0.52 2507  93  61  11 0.03
Fri 06/26 20Z 0.49 2408  92  66  12 0.14
Fri 06/26 21Z 0.50 2710  91  73  12 0.17
Fri 06/26 22Z 0.46 2813  91  73  12 0.16
Fri 06/26 23Z 0.36 3012  87  64  12 0.05
Sat 06/27 00Z 0.38 3013  89  56  11 0.01
Sat 06/27 01Z 0.39 2913  93  55  11 0.00
Sat 06/27 02Z 0.27 3010  91  49  11 0.00
Sat 06/27 03Z 0.28 2910  91  46  11 0.00
Sat 06/27 04Z 0.24 2909  93  47  11 0.00
Sat 06/27 05Z 0.22 3009  93  46  11 0.00
Sat 06/27 06Z 0.20 3008  92  45  11 0.00
Sat 06/27 07Z 0.19 3008  93  45  11 0.00
Sat 06/27 08Z 0.18 3007  94  45  11 0.00
Sat 06/27 09Z 0.17 3007  95  46  11 0.00
Sat 06/27 10Z 0.13 3006  96  49  10 0.00
Sat 06/27 11Z 0.07 3205  95  48  10 0.00
Sat 06/27 12Z 0.02 3404  94  47  11 0.00
Sat 06/27 13Z 0.04 3203  95  52  10 0.00
Sat 06/27 14Z 0.03 3302  94  54  10 0.00
Sat 06/27 15Z 0.05 2801  95  55  11 0.01
Sat 06/27 16Z 0.05 2701  95  55  11 0.03
Sat 06/27 17Z 0.07 2601  95  58  11 0.04
Sat 06/27 18Z 0.09 2802  95  54  11 0.04
Sat 06/27 19Z 0.07 3001  94  51  11 0.02
Sat 06/27 20Z 0.05 3302  93  48  11 0.03
Sat 06/27 21Z 0.05 3302  93  49  12 0.04
Sat 06/27 22Z 0.06 3402  93  50  12 0.04
Sat 06/27 23Z 0.06 3503  92  49  12 0.03
Sun 06/28 00Z 0.09 0203  92  48  12 0.03
Sun 06/28 01Z 0.09 0103  93  50  11 0.01
Sun 06/28 02Z 0.11 0304  92  51  11 0.01
Sun 06/28 03Z 0.13 0304  93  54  11 0.00
Sun 06/28 04Z 0.11 0205  94  56  11 0.00
Sun 06/28 05Z 0.10 0205  95  60  11 0.00

Run total areal avg QPF for the Central_Greens is: 1.57 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