NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260727_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 07/27 18Z 1.25 2403  83  61  14 0.00
Mon 07/27 19Z 0.97 2403  83  60  14 0.06
Mon 07/27 20Z 0.50 2204  83  65  14 0.08
Mon 07/27 21Z 0.26 2103  82  70  15 0.04
Mon 07/27 22Z 0.06 1704  81  69  15 0.04
Mon 07/27 23Z 0.05 1607  81  65  15 0.02
Tue 07/28 00Z 0.14 1808  83  66  14 0.00
Tue 07/28 01Z 0.22 1910  82  63  14 0.00
Tue 07/28 02Z 0.33 2012  83  59  14 0.00
Tue 07/28 03Z 0.20 1912  84  56  14 0.00
Tue 07/28 04Z 0.27 2013  86  62  14 0.00
Tue 07/28 05Z 0.24 2013  91  64  14 0.00
Tue 07/28 06Z 0.20 1912  91  63  14 0.00
Tue 07/28 07Z 0.13 1911  87  62  14 0.00
Tue 07/28 08Z 0.16 1912  87  73  14 0.00
Tue 07/28 09Z 0.07 1811  85  73  14 0.00
Tue 07/28 10Z 0.07 1812  85  68  14 0.00
Tue 07/28 11Z 0.13 1912  89  68  14 0.00
Tue 07/28 12Z 0.10 1811  90  70  14 0.00
Tue 07/28 13Z 0.06 1811  90  72  14 0.00
Tue 07/28 14Z 0.03 1712  90  70  14 0.00
Tue 07/28 15Z 0.03 1713  93  70  14 0.01
Tue 07/28 16Z 0.06 1614  96  71  14 0.01
Tue 07/28 17Z 0.12 1515  97  68  14 0.01
Tue 07/28 18Z 0.28 1417  98  66  14 0.01
Tue 07/28 19Z 0.23 1518  98  74  14 0.04
Tue 07/28 20Z 0.20 1518  98  80  14 0.08
Tue 07/28 21Z 0.10 1620  98  85  14 0.12
Tue 07/28 22Z 0.14 1621  97  88  14 0.21
Tue 07/28 23Z 0.18 1523  98  85  14 0.14
Wed 07/29 00Z 0.21 1524  98  85  14 0.06
Wed 07/29 01Z 0.14 1624  99  84  14 0.11
Wed 07/29 02Z 0.12 1624  95  82  13 0.11
Wed 07/29 03Z 0.15 1626  91  82  13 0.10
Wed 07/29 04Z 0.25 1525  89  84  13 0.01
Wed 07/29 05Z 0.34 1427  89  87  13 0.01
Wed 07/29 06Z 0.40 1429  87  88  12 0.01
Wed 07/29 07Z 0.45 1328  86  87  12 0.01
Wed 07/29 08Z 0.53 1330  85  87  12 0.01
Wed 07/29 09Z 0.56 1331  83  83  12 0.01
Wed 07/29 10Z 0.59 1233  82  80  12 0.01
Wed 07/29 11Z 0.60 1234  76  78  13 0.01
Wed 07/29 12Z 0.59 1235  72  79  13 0.00
Wed 07/29 13Z 0.60 1134  70  85  13 0.00
Wed 07/29 14Z 0.61 1133  69  87  13 0.00
Wed 07/29 15Z 0.66 1133  73  83  13 0.01
Wed 07/29 16Z 0.79 1133  79  79  12 0.01
Wed 07/29 17Z 0.81 1132  79  84  12 0.01
Wed 07/29 18Z 0.90 1032  85  89  11 0.02
Wed 07/29 19Z 0.98 1032  89  85  11 0.01
Wed 07/29 20Z 1.06 0932  92  86  11 0.01
Wed 07/29 21Z 1.02 0933  90  80  11 0.02
Wed 07/29 22Z 1.02 0934  91  85  11 0.03
Wed 07/29 23Z 1.07 0935  94  86  11 0.04
Thu 07/30 00Z 0.99 0935  95  85  11 0.05
Thu 07/30 01Z 0.98 0936  96  85  11 0.08
Thu 07/30 02Z 0.93 0937  95  73  12 0.11
Thu 07/30 03Z 0.81 1035  95  70  12 0.04
Thu 07/30 04Z 0.74 1033  96  76  12 0.04
Thu 07/30 05Z 0.70 1032  94  79  12 0.04

Run total areal avg QPF for the Central_Greens is: 1.85 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