Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260621_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)
=== ===== === ==== ==== === === === ====
Sun 06/21 18Z 3.53 2908  88  75   9 0.00
Sun 06/21 19Z 1.18 2910  88  75   9 0.05
Sun 06/21 20Z 0.42 3013  83  71   9 0.17
Sun 06/21 21Z 0.56 2914  82  77   9 0.02
Sun 06/21 22Z 0.47 2912  84  74  10 0.01
Sun 06/21 23Z 0.46 2914  84  78  10 0.01
Mon 06/22 00Z 0.48 2915  85  74  10 0.02
Mon 06/22 01Z 0.44 3017  84  60  10 0.01
Mon 06/22 02Z 0.41 3016  85  49  10 0.00
Mon 06/22 03Z 0.38 3015  86  51  10 0.00
Mon 06/22 04Z 0.32 3014  83  44  10 0.00
Mon 06/22 05Z 0.24 3113  82  39  10 0.00
Mon 06/22 06Z 0.20 3110  81  33  10 0.00
Mon 06/22 07Z 0.25 2910  83  33  10 0.00
Mon 06/22 08Z 0.25 2809  82  28  10 0.00
Mon 06/22 09Z 0.30 2710  85  26   9 0.00
Mon 06/22 10Z 0.36 2710  87  25   9 0.00
Mon 06/22 11Z 0.42 2711  86  26   9 0.00
Mon 06/22 12Z 0.34 2709  80  21   9 0.00
Mon 06/22 13Z 0.21 2806  73  17  10 0.00
Mon 06/22 14Z 0.12 2703  69  19  10 0.00
Mon 06/22 15Z 0.25 2405  78  27   9 0.00
Mon 06/22 16Z 0.29 2305  76  52   9 0.00
Mon 06/22 17Z 0.36 2109  78  82   9 0.00
Mon 06/22 18Z 0.41 2112  85  89   8 0.01
Mon 06/22 19Z 0.22 2011  81  96   8 0.03
Mon 06/22 20Z 0.16 2010  81  95   8 0.04
Mon 06/22 21Z 0.15 1911  86  91   8 0.05
Mon 06/22 22Z 0.14 1813  88  95   9 0.05
Mon 06/22 23Z 0.13 1614  93  94   9 0.13
Tue 06/23 00Z 0.20 1418  94  92   9 0.23
Tue 06/23 01Z 0.27 1317  96  96   9 0.28
Tue 06/23 02Z 0.32 1321  96  97   9 0.24
Tue 06/23 03Z 0.32 1323  97  99   9 0.28
Tue 06/23 04Z 0.28 1422  97  96  10 0.16
Tue 06/23 05Z 0.23 1421  97  99  11 0.07
Tue 06/23 06Z 0.19 1417  98  97  11 0.23
Tue 06/23 07Z 0.10 1512  98  96  11 0.09
Tue 06/23 08Z 0.10 1508  98  94  11 0.03
Tue 06/23 09Z 0.08 1703  99  92  11 0.02
Tue 06/23 10Z 0.06 0002  99  90  10 0.01
Tue 06/23 11Z 0.05 3505  99  91  10 0.00
Tue 06/23 12Z 0.05 3508  98  81  10 0.00
Tue 06/23 13Z 0.05 3511  98  59  10 0.00
Tue 06/23 14Z 0.05 3513  97  45   9 0.00
Tue 06/23 15Z 0.03 3514  96  37   9 0.00
Tue 06/23 16Z 0.04 3416  91  30  10 0.00
Tue 06/23 17Z 0.08 3417  89  24  10 0.00
Tue 06/23 18Z 0.10 3419  84  19  10 0.00
Tue 06/23 19Z 0.17 3419  84  18  10 0.00
Tue 06/23 20Z 0.30 3419  85  17  10 0.00
Tue 06/23 21Z 0.20 3418  83  16  10 0.00
Tue 06/23 22Z 0.22 3317  83  20  10 0.00
Tue 06/23 23Z 0.29 3319  85  37  10 0.02
Wed 06/24 00Z 0.33 3222  88  49  10 0.02
Wed 06/24 01Z 0.43 3224  84  33   9 0.00
Wed 06/24 02Z 0.42 3224  85  27   9 0.00
Wed 06/24 03Z 0.35 3223  87  17   9 0.00
Wed 06/24 04Z 0.30 3222  90  15   9 0.00
Wed 06/24 05Z 0.28 3222  90  21   9 0.00

Run total areal avg QPF for the Central_Greens is: 2.28 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