Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260622_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)
=== ===== === ==== ==== === === === ====
Mon 06/22 12Z 0.24 2307  84  53   9 0.00
Mon 06/22 13Z 0.25 2207  82  50  10 0.00
Mon 06/22 14Z 0.32 2107  82  43  10 0.00
Mon 06/22 15Z 0.46 2106  80  46  10 0.00
Mon 06/22 16Z 0.31 2006  75  62  10 0.00
Mon 06/22 17Z 0.28 1809  76  79  10 0.00
Mon 06/22 18Z 0.34 1911  82  95  10 0.01
Mon 06/22 19Z 0.20 1911  89  95   9 0.07
Mon 06/22 20Z 0.14 1814  93  96   9 0.15
Mon 06/22 21Z 0.12 1817  96  96   9 0.13
Mon 06/22 22Z 0.08 1717  94  93   9 0.06
Mon 06/22 23Z 0.08 1617  89  95   9 0.01
Tue 06/23 00Z 0.12 1518  89  97   9 0.02
Tue 06/23 01Z 0.14 1517  93  99   9 0.03
Tue 06/23 02Z 0.16 1517  95  96  10 0.05
Tue 06/23 03Z 0.13 1517  97  98  10 0.04
Tue 06/23 04Z 0.12 1517  97  94  11 0.04
Tue 06/23 05Z 0.10 1617  98  94  11 0.03
Tue 06/23 06Z 0.12 1713  98  93  11 0.03
Tue 06/23 07Z 0.08 1709  99  87  12 0.02
Tue 06/23 08Z 0.05 1605  99  87  12 0.02
Tue 06/23 09Z 0.04 1504  99  92  12 0.01
Tue 06/23 10Z 0.05 1303  99  95  12 0.01
Tue 06/23 11Z 0.04 1301  99  95  11 0.01
Tue 06/23 12Z 0.04 3401  99  89  11 0.01
Tue 06/23 13Z 0.05 3304  99  87  11 0.00
Tue 06/23 14Z 0.06 3407  98  84  11 0.00
Tue 06/23 15Z 0.06 3509  97  77  11 0.00
Tue 06/23 16Z 0.06 3510  95  60  10 0.00
Tue 06/23 17Z 0.04 3510  94  52  10 0.00
Tue 06/23 18Z 0.03 3511  92  38  10 0.00
Tue 06/23 19Z 0.03 3511  90  23  10 0.00
Tue 06/23 20Z 0.06 3512  88  15  11 0.00
Tue 06/23 21Z 0.07 3513  84  10  11 0.00
Tue 06/23 22Z 0.07 3515  79   7  11 0.00
Tue 06/23 23Z 0.06 3516  74   6  11 0.00
Wed 06/24 00Z 0.09 3418  77   7  11 0.00
Wed 06/24 01Z 0.11 3420  82  10  10 0.00
Wed 06/24 02Z 0.08 3421  87  10  10 0.00
Wed 06/24 03Z 0.03 3421  87  11  10 0.00
Wed 06/24 04Z 0.07 3521  88  14  10 0.00
Wed 06/24 05Z 0.05 3521  89  17   9 0.00
Wed 06/24 06Z 0.08 3522  88  16   9 0.00
Wed 06/24 07Z 0.10 3521  85  17   9 0.00
Wed 06/24 08Z 0.07 3520  84  20   9 0.00
Wed 06/24 09Z 0.04 3419  82  18   9 0.00
Wed 06/24 10Z 0.14 3320  81  17   9 0.00
Wed 06/24 11Z 0.22 3221  82  21   9 0.00
Wed 06/24 12Z 0.29 3221  84  22   8 0.00
Wed 06/24 13Z 0.33 3221  85  26   8 0.00
Wed 06/24 14Z 0.41 3120  85  27   8 0.00
Wed 06/24 15Z 0.59 3119  84  30   8 0.00
Wed 06/24 16Z 1.10 3017  87  37   8 0.00
Wed 06/24 17Z 1.68 2916  90  38   8 0.00
Wed 06/24 18Z 3.21 2816  87  36   8 0.00
Wed 06/24 19Z 5.04 2816  85  44   9 0.00
Wed 06/24 20Z 6.72 2816  82  44   9 0.00
Wed 06/24 21Z 6.37 2917  80  41   9 0.00
Wed 06/24 22Z 3.71 2919  85  34   9 0.00
Wed 06/24 23Z 1.86 3020  86  30   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.75 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