Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260622_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)
=== ===== === ==== ==== === === === ====
Mon 06/22 18Z 0.43 2014  86  86   9 0.00
Mon 06/22 19Z 0.40 2016  88  97   8 0.04
Mon 06/22 20Z 0.28 2016  91  92   8 0.07
Mon 06/22 21Z 0.15 1915  89  91   9 0.04
Mon 06/22 22Z 0.13 1815  90  95   9 0.03
Mon 06/22 23Z 0.10 1614  87  97   9 0.04
Tue 06/23 00Z 0.17 1515  88  99   9 0.04
Tue 06/23 01Z 0.15 1517  93  98  10 0.05
Tue 06/23 02Z 0.10 1518  96  97  10 0.04
Tue 06/23 03Z 0.09 1518  98  96  11 0.05
Tue 06/23 04Z 0.09 1617  98  98  11 0.04
Tue 06/23 05Z 0.09 1615  98  99  11 0.05
Tue 06/23 06Z 0.11 1514  98  99  11 0.04
Tue 06/23 07Z 0.11 1511  98  96  11 0.03
Tue 06/23 08Z 0.09 1508  98  95  11 0.02
Tue 06/23 09Z 0.07 1705  99  94  11 0.01
Tue 06/23 10Z 0.07 2203  99  91  12 0.01
Tue 06/23 11Z 0.09 2704  99  81  12 0.01
Tue 06/23 12Z 0.08 3105  99  70  11 0.00
Tue 06/23 13Z 0.06 3307  98  54  11 0.01
Tue 06/23 14Z 0.07 3409  98  40  11 0.00
Tue 06/23 15Z 0.07 3510  96  25  10 0.00
Tue 06/23 16Z 0.07 3511  95  15  10 0.00
Tue 06/23 17Z 0.03 3511  93  12  10 0.00
Tue 06/23 18Z 0.03 3512  90  11  10 0.00
Tue 06/23 19Z 0.05 3512  87   8  11 0.00
Tue 06/23 20Z 0.07 3513  87   8  10 0.00
Tue 06/23 21Z 0.05 3412  84   7  10 0.00
Tue 06/23 22Z 0.10 3513  81   6  11 0.00
Tue 06/23 23Z 0.09 3513  81   6  10 0.00
Wed 06/24 00Z 0.08 3415  82   9  10 0.00
Wed 06/24 01Z 0.07 3417  84  11  10 0.00
Wed 06/24 02Z 0.15 3419  89  15  10 0.00
Wed 06/24 03Z 0.24 3320  87  18   9 0.00
Wed 06/24 04Z 0.19 3321  85  24   9 0.00
Wed 06/24 05Z 0.15 3321  87  31   9 0.00
Wed 06/24 06Z 0.07 3419  87  27   9 0.00
Wed 06/24 07Z 0.07 3418  87  20   9 0.00
Wed 06/24 08Z 0.07 3418  87  18   9 0.00
Wed 06/24 09Z 0.10 3315  86  18   9 0.00
Wed 06/24 10Z 0.17 3215  85  20   9 0.00
Wed 06/24 11Z 0.23 3216  83  19   9 0.00
Wed 06/24 12Z 0.35 3017  86  17   8 0.00
Wed 06/24 13Z 0.43 3019  88  20   8 0.00
Wed 06/24 14Z 0.47 3019  87  30   8 0.00
Wed 06/24 15Z 0.74 3017  86  34   8 0.00
Wed 06/24 16Z 2.06 3015  88  34   8 0.00
Wed 06/24 17Z 2.70 2915  91  36   8 0.00
Wed 06/24 18Z 2.43 2814  89  45   9 0.00
Wed 06/24 19Z 3.43 2814  87  45   9 0.00
Wed 06/24 20Z 3.79 2813  84  46   9 0.00
Wed 06/24 21Z 3.28 2814  81  41  10 0.00
Wed 06/24 22Z 2.62 2915  79  34  10 0.00
Wed 06/24 23Z 1.83 3016  78  31  10 0.00
Thu 06/25 00Z 1.44 3016  80  29  10 0.00
Thu 06/25 01Z 1.40 3016  82  28  10 0.00
Thu 06/25 02Z 1.14 3015  84  31   9 0.00
Thu 06/25 03Z 0.76 3015  84  31   9 0.00
Thu 06/25 04Z 0.63 3015  84  29   9 0.00
Thu 06/25 05Z 0.52 3014  84  26   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.62 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